Being president of the United States comes with plenty of benefits, but Donald Trump seems to be rejecting one of the best: a personal plane. And not just any private jet—after all, Trump's got a Boeing 757 to call his own. The president-elect took to Twitter this morning to blast Air Force One, perhaps the most sophisticated aircraft on the planet:

Boeing's current contract to provide the next generation of the presidential plane is for $170 million, but the Air Force plans to ask the Seattle giant to heavily modify the two 747-8 jets it has on order. The current budget for the Presidential Aircraft Recapitalization program puts the price tag at $2.9 billion—a shocking figure, since Boeing lists the standard 747-8 for $357 million. And that only takes the program to 2021, the standard 'five years out'. The planes aren't due to enter service until 2023 or 2024, so costs will rise.

"The $4 billion figure looks reasonable," says Mark Cancian, a senior advisor at the Center for Strategic and International Studies, who previously oversaw Department of Defense acquisitions at the White House Office of Management and Budget. OK, "reasonable" may not seem right to anyone unfamiliar with American military budgets, but that doesn't mean Trump's right to say "costs are out of control."

"Given the extraordinary capabilities that they want in this aircraft, that’s not an unreasonable cost for two," Cancian says.

It doesn't help that the Air Force has just one major American aircraft manufacturer to deal with—Europe's Airbus didn't even bother to enter a bid for this contract—but there's plenty to explain the price tag. The Air Force's "budget item justification" states the "Boeing 747-8 commercial aircraft will be uniquely modified to provide the President, staff, and guests with safe and reliable air transportation with the equivalent level of communications capability and security available in the White House."

That means packing these planes with electrical upgrades, with backup power units, secure communications systems, and military spec flight and navigation controls. For the two 747-200s the president uses now, that includes multi-frequency radios capable of air-to-air, air-to-ground, and satellite communications. It takes years of serious spending to develop and integrate all that into a new plane (the 747-8 entered service in 2011). Especially since you've got to harden every bit of it to shrug off the electromagnetic waves that can result from nuclear explosions and tend to fry electronics.

Reducing dependence on foreign airports means reducing risk factors, so Air Force One comes with stairs built into the doors (those came in handy for President Obama in China in September). Same goes for luggage—the plane has built in handling equipment instead of relying on airport infrastructure. If the fuel tanks that power its four engines tap out, aerial refueling can keep the jet aloft. "That's not just for convenience," says Cancian: Landing to top off introduces more security concerns.

Naturally, the interior is pretty specialized, too. According to Boeing, the current 747-200 offers a dining room, quarters for the president and first lady, and offices for staff, including one that converts to a medical facility. The galleys can feed 100 people at once—and they don't eat your standard economy class fare.

That may seem plenty sufficient for any world leader's ego and safety, but the current jets, which entered service in 1990, will hit retirement age in 2017. The new planes won't take off until 2024, so the current fleet will have to fly a bit longer anyway. It’s not clear if Trump will continue to use them, or if he’d prefer to travel on his own Boeing 757—if he can convince the Secret Service and White House Military Office to agree.

Now, there is one plane more capable than Air Force One, the plane to climb aboard if it really looks like the world's ending: the Boeing E-4. Reflective of the Cold War paranoia in which they came to life, these extra-heavily modified 747-200s are basically the bunker under the White House. Midair refueling can keep them airborne for more than a week; flight time comes down to engine lubricants and onboard supplies of food. Interior space goes to equipment and supplies instead of fancy suites. They're built to withstand electromagnetic pulses. When the president travels abroad on Air Force One, an E-4 deploys to a nearby airfield just in case.

Whatever Donald Trump does with Boeing's contract, it is true the US spends (or wastes, depending on your point of view) extraordinary sums of money on this stuff. By contrast, other world leaders often travel on chartered or regular airlines. The British Prime Minister has access to a $12 million converted Airbus A330 that's so spartan, it’s been dubbed “Austerity Force One”. Trump may not want to spend $4bn on new planes, but don't expect him to rough it.