Never mind that the gift of a half-dozen MiG-29 jets came with a steep price tag for required repairs: $209 million, payable to Russia. The Serbian president heaped praise on Russian President Vladi­mir Putin.

The gift of the jets encapsulates Russian strategy in Serbia — and much of the world. The Kremlin has built a methodical but low-cost influence campaign that is reaping rocketing returns.

The thrifty approach helps explain how a country with a faltering economy, a country President Barack Obama once derided as a “regional power,” has been able to wield outsize influence and confound its adversaries.

Russia and the West are engaged in a pitched battle for the allegiance of Serbia, a pivotal Balkan nation that has declared a desire to join the European Union but also counts Russia as an ally.

While the West is spending far more cash — in Europe’s case, as much as $11.8 billion in 2016, totaling up aid, investments and trade — Russia’s presence is far more penetrating. Across Serbian life, the Kremlin has been expert at finding ways to attract friends and good publicity at bargain prices. And by appealing to ordinary Serbs, it has gained a more deeply rooted hold than if it had pursued its push solely among Serbian leaders.

Russia built an emergency relief center that elicits gratitude every time Serbia faces floods or fires — but that Western officials worry might be a spy hub. It has muscle-bound allies in a Serbian biker gang that is closely linked to Putin and helped Russia seize Crimea from Ukraine in 2014. Russian state media broadcast Serbian-language reports, such as one suggesting NATO and the Islamic State were plotting together to spread chaos at the World Cup.

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“The West is investing enormous amounts of money in Serbia, but psychologically they are small when you compare them to the MiG factor,” said Petar Vojinovic, editor of Tango Six, a Serbian aviation-news outlet.

Although Russia emphasizes its supposedly unbreakable ties with Serbia, cemented by shared Orthodox and Slavic heritage, that narrative glosses over much of the 20th century. The relationship was frosty after Yugoslavia’s communist-era leader Josip Broz Tito broke with the Soviet Union in 1948. During the ethnic clashes and NATO bombing in the Balkans in the 1990s, Russia was mostly sidelined by its own domestic turmoil. It was only at the turn of the millennium, when Russia supported Serbia in its opposition to Kosovo’s drive for independence, that relations began to warm again.

“This image of brotherhood was nurtured through soft-power channels,” said Vuk Vuksanovic, a London School of Economics researcher who previously worked at the Serbian Ministry of Foreign Affairs.

Flattering depictions of Russia are plentiful in Serbia’s raucous tabloids and on the airwaves, thanks to Serbian-language bulletins from Russia’s state-run Sputnik news agency, which opened in Belgrade in 2015.

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“It’s not foreign meddling. We don’t feel the Russian perspective is foreign,” said Nikola Vrzic, who hosts a radio show on Sputnik and is also an editor at the pro-Russian Pecat newsweekly. Pictures of a glowering Putin crowded the walls at the magazine’s offices. “When you have a Western perspective, that’s foreign meddling,” Vrzic said.

Russia’s tricolor flag appears intertwined with Serbia’s alongside highways, on billboards sponsored by Russia’s Gazprom energy company. E.U. funds paid for many of the roads, but the tiny blue-and-yellow European flag goes down as soon as construction is complete.

Russia has come to dominate Serbia’s oil and natural gas market — a fraction of the overall economy, but a key one for the country’s security. Serbia imports 75 percent of its natural gas, all of it from Russia. Since 2008, Moscow has controlled domestic production, too, after Serbia’s national energy company was sold to Gazprom for a bargain price. The profits help Russia’s broader influence efforts pay for themselves.

Russia also has a strong presence at church. Many Serbian Orthodox priests meet frequently with senior Russian political leaders. In their sermons, they play up the common religious heritage and thank the Kremlin for trying to thwart independence for Kosovo, which the Serbian church considers its ancestral home. The construction of an Orthodox church in a Russian style northwest of Belgrade attracted tens of thousands of dollars in donations after it was dubbed “Putin’s church.”

As Serbians have begun to encounter Russia everywhere they turn, Moscow’s inroads have alarmed some local observers.

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“It’s not just that the Russians are marching in — it’s that they are welcomed by too many people in society,” said Jelena Milic, director of the Center for Euro-

Atlantic Studies, a think tank that advocates closer ties with the West.

Among the signs of Moscow’s success: Many Serbs mistakenly believe Russia is their biggest partner for trade, aid and the military, according to opinion polls.

In fact, 65 percent of their country’s trade is with the E.U., while only 6.7 percent is with Russia. Serbian soldiers trained more than 20 times last year with NATO members, compared with twice with Russian counterparts. And the E.U. and its members offered more than $600 million in aid to Serbia in 2016, the latest year figures are available, 50 times as much as the Kremlin. (The United States, China and the Persian Gulf states have also made major investments in the country.)

In Serbia, “the Russians are giving nothing and getting a lot in the deal,” said Bosko Jaksic, a ­foreign policy columnist at Politika, a Serbian daily. “Big politics can change in an instant. If you target the cells of people’s brains, it’s much more dangerous.”

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Russia’s interest relates to Serbia’s geography — perched between East and West. Of Serbia’s eight neighbors, five are NATO members. Four are in the E.U., and several more are working toward accession.

Moscow already has secured Serbia’s commitment that it won’t seek to join NATO or join E.U. sanctions against Russia. Many Western officials think Moscow intends to deter Serbia’s E.U. membership aspirations altogether.

The potential for Russian mischief has increased since Serbia’s Vucic and Kosovo President Hashim Thaci signaled in August that they are open to normalizing relations. The two leaders have been working on a deal that may involve a land swap and Serbian recognition of Kosovo, the largely ethnically Albanian territory that declared independence from Belgrade in 2008 with Western backing.

Resolving their differences is a prerequisite of E.U. membership for both countries, even as some E.U. leaders express nervousness about the land swap. But continuation of the rift benefits Russia, and although Moscow has said it is open to a deal, officials close to the Serbian president fear the Kremlin may try to be a spoiler.

The Russian ambassador to Serbia clearly dangled a carrot last month when he confirmed that Putin would visit Belgrade this fall, with the added enticement of “hundreds” of Russian government officials and businesspeople.

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“We have seen Russian attempts to interfere and to influence,” said NATO Secretary General Jens Stoltenberg, who visited Vucic in Belgrade this week during joint NATO-Serbia emergency response exercises. “It is extremely important that we don’t forget the Balkans, because we have seen before that conflicts in the Balkans can trigger devastating wars.”

Analysts who have assessed the potential for Russian interference in Serbia have zeroed in on the Russian-Serbian Humanitarian Center in the southern city of Nis. The Russian-funded center, built in 2012, has served as a base for relief efforts. On a recent afternoon, Hungarian volunteers were practicing how to excavate bodies from an urban building collapse under the watchful eyes of Russian instructors. Inside, cots and stretchers were piled next to inflatable motorboats — all of which have drawn grateful coverage in the Serbian press when deployed during floods and wildfires.

European and U.S. security officials, however, say the center, just 75 miles from Camp Bondsteel, the main NATO base in Kosovo, may be an intelligence-gathering outpost — or could be converted into one if Serbia grants the Kremlin’s request for diplomatic status for its workers there.

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Russia has dismissed the accusations.

“No, we’re not a spy center,” said Viktor Gulevich, a senior official from the Russian Ministry of Emergency Situations who has run the center since last year. “If people are scared of this, then they need to go to psychoanalysis, because it’s all in their heads. They have a phobia.”

Gulevich said the center wants diplomatic status for its workers to stretch its budget by saving on taxes and import duties, nothing more.

“We’re all Slavs,” Gulevich said. “We’re close. We have a relationship like brothers.”

Speaking on the condition of anonymity to discuss sensitive security concerns, officials from the United States, E.U. and NATO said the center has advanced communications equipment that may go beyond its needs for emergency rescues. Diplomatic immunity, they worry, would make it even harder to prevent troublemaking.

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“If [Serbia] allows Russia to create some kind of a special center for espionage or other nefarious activities, it will lose control over part of its territory,” Hoyt Yee, then the top State Department official for the region, testified before a Senate Foreign Relations subcommittee last year.

Officials close to Vucic say that if they were forced to give in to Russia on the status of the center, their window to join the E.U. could snap shut.

Other low-cost influence efforts have come through Russian proxies.

Sasa Savic, a nationalist with a tattoo of an Orthodox church on his right forearm, leads the Serbian Night Wolves, a branch of a Russian motorcycle gang supported by the Kremlin. Savic said he has met Putin six times.

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“He’s taking Russia up from the ashes like a phoenix,” Savic said.

As Russia took steps to annex Ukraine’s Crimea in 2014, the Night Wolves traveled to the peninsula to offer what Savic said was protection against potential aggression from pro-Kiev forces.

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“We just wanted to stop and prevent the possibility of fratricide, just like what happened in Yugoslavia,” Savic said.

The U.S. Treasury Department imposed sanctions on the Russian Night Wolves for “intimidation and criminal activities within Ukraine” as Russia annexed Crimea, charging members with abducting and assaulting a Ukrainian border guard and helping to storm a Ukrainian naval base, among other allegations.

This year, with a grant from the Kremlin, the Russian and Serbian bike clubs organized a road trip from Belgrade into the ethnic-Serb-controlled part of Bosnia. The trip appeared to be largely a mix of church tours and late-night drinking with local nationalists. But it sparked worries from Bosnian authorities that the bikers were laying the groundwork for more clashes over national borders. Savic was banned from Bosnia as a national security threat — which he said was ridiculous. He denied he was an agent of Putin and insisted that the Serbian bikers paid their own way.

“We don’t have anything other than mutual respect,” he said. “He respects us for our work, I respect him for being a strong leader — nothing more than that.”

A different pair of Serbian and Russian nationalist groups were behind a paramilitary youth camp in rural western Serbia, where teenagers clad in camouflage learned gun and knife skills from Russian and Serbian trainers.

The organizers — a Serbian war veterans association and the Russian ENOT Corp., which boasts of fighting alongside pro-Russian separatists in eastern Ukraine — told local media that a Russian military attache paid a visit to the camp in August and that the Russian Embassy in Serbia had prepared “gifts” for the children.

Serbian officials shut the camp down.

Vucic’s tightrope act was on display as he celebrated the delivery of the Russian fighter jets days later. “You cannot have military camps organized by nongovernmental organizations,” he said.

The ENOT Corp. and the Russian Embassy did not respond to requests for comment. The Serbian veterans group, in a rambling and homophobic statement on its website, said Serbia faced a choice between military marches and the gay parades that closer cooperation with Europe would bring.

Serbian leaders insist that they need not pick sides.

“It is very difficult to tackle people’s sentiments and people’s emotions,” Vucic said in an interview. “But even when we go to Russia, it does not mean we are leaving our E.U. path.”

But Brussels officials, watching Russian actions in Serbia with alarm, say the country’s Western course is hardly guaranteed. Some have even raised the question of whether to suspend membership talks with Belgrade over concerns that Vucic has not imposed sanctions aligned with Europe’s and has been dragging his feet on rule-of-law issues they raised with him.

The result, for Russia, would be a diplomatic coup — on the cheap.