As President Donald Trump continued his weeks-long push for Congress to give him the funds he demanded for his border wall, he stressed a false claim about how much illegal immigration costs the country.

"It's so insignificant compared to what we’re talking about. You know, I've heard numbers as high as $275 billion we lose on illegal immigration," he said at a Cabinet meeting at the White House on Wednesday. "The $5 billion, $5.6 billion approved by the House is such a small amount compared to the level of the problem."

Trump has repeatedly used that figure to argue that the wall would pay for itself, despite originally promising Mexico would foot the bill. In early December, he said illegal immigration costs $250 billion per year. On Dec. 18, he said it was "more than $200 billion per year." At a bill signing event on Dec. 20, he said, "Illegal immigration costs our nation $275 billion a year."

What are the facts behind the economic impact of immigrants? We checked Trump's figures with immigration and tax policy experts across the political spectrum,who said he was exaggerating, at best.

"That $200 billion figure does seem inflated to me," said Randy Capps, director for research for U.S. programs at the nonpartisan Migration Policy Institute.

"A little high," said Robert Rector, a senior research fellow with the Heritage Foundation.

"It sounds extraordinarily high to me," said Meg Wiehe, deputy director at the nonpartisan Institute on Taxation and Economic Policy (ITEP).

"Frankly absurd," David Dyssegaard Kallick, the deputy director of the nonpartisan Fiscal Policy Institute, told NBC News.

If Trump's wrong, what's the true cost?

Conservative groups like the Heritage Foundation have sought to put a price tag on illegal immigration amid lobbying efforts against legalization, but none have pegged it as high as Trump's estimate.

Rector said his 2013 estimate pegged the cost of undocumented immigrants — the cost of services received minus their tax contributions — was about $54 billion a year.

A precise cost is nearly impossible to ascertain, many experts said. That's in part because undocumented immigrants operate within the shadows, leaving their full fiscal contributions — and use of taxpayer-funded resources — at least somewhat unknown.

"It's really hard to calculate anyone’s 'net cost' or 'net benefit.' We all use all kinds of services, from roads to military protection. How do we apportion what part of that is something I or you or an immigrant use?" said Kallick.

Overall, there is a broad misunderstanding of how much undocumented immigrants contribute to America's balance sheets, and what taxpayer-funded benefits they receive, the experts interviewed by NBC News said.

"Undocumented immigrants are incredible contributors to our economy and are not eligible for public benefits that people think they come here for," Wiehe said.

An estimated half of the nation's undocumented immigrants are believed to be working under fake Social Security numbers, which means they are paying taxes and into Social Security. The ITEP estimates that state and local governments take in $11.74 billion a year from undocumented immigrants.

Wiehe added that undocumented immigrants are also not eligible for the federal earned income tax credit, so they're taxed at higher rates than similar low-income Americans.

Capps said that undocumented immigrants also pay taxes in other ways: paying sales taxes on items they purchase, and funding property taxes through rent payments, too.

Meanwhile, undocumented immigrants are not eligible for Social Security and the vast majority of taxpayer-funded welfare programs like food stamps and cash assistance, according to Capps, the expert with the Migration Policy Institute.

There are some notable exceptions: many receive medical care through emergency rooms and some undocumented immigrants are able to receive taxpayer-funded benefits through the Woman, Infants, and Children program, which helps provide food and formula for low-income pregnant and breastfeeding mothers and young children.

The biggest costs to taxpayers, experts told NBC News, come from public education, which all students are eligible to receive regardless of immigration status.

Researchers and advocates are split on whether it's fair to view the education and welfare of U.S. citizen children born to undocumented immigrants as part of the costs of undocumented immigrants, but most say it's worth considering at least. Rector said it was a big factor in his estimate.

"Public education is where the real big cost comes in," Capps said. "The amount of taxes that the parents pay on their earnings, that they pay through property taxes — passed through on their rent — it's not going to be as much as is spent on public education for their kids and food stamps for their kids."

Still, Capps added, second generation immigrants — the U.S.-born children of undocumented immigrants — often go on to do far better than their parents and can boost the American economy.

"They'll be paying it back over the long run, some of that cost — particularly like public schooling — pays for itself," Capps said. "Some people will just focus on how much more unauthorized immigrants cost than they're paying, but it ignores the broader economic picture."

Kallick said the debate over costs was not relevant to the necessary fiscal conversations the country is having, particularly in a country with citizens that operates on a net negative — running on a deficit.

"Fundamentally I think it’s the wrong question. The right question for undocumented immigrants and any group is, 'Are they paying their fair share of taxes and getting their fair share of service?'" Kallick said. "You’re talking about people who work for very low wages and are excluded from nearly all social services. It takes a real act of will to say they're exploiting us."

CORRECTION (Dec. 22, 2018, 1:15 p.m. ET): A earlier version of this article misstated the name of the organization where David Dyssegaard Kallick works. It is the Fiscal Policy Institute, not the Fiscal Policy Center.