A conservative think tank's estimate that immigration reform will cost American taxpayers trillions of dollars has highlighted a growing split inside the Republican Party over how to address the more than 11 million illegal immigrants who now reside in the United States.

A report by Robert Rector, a senior research fellow at the Heritage Foundation, found that legalizing those now here illegally and providing them with a pathway to citizenship will cost the nation $6.3 trillion over the next 50 years because most of those who would be eligible are undereducated, earn low wages and would require more federal benefits than they would contribute in taxes.

The report, relesaed Monday, doesn't put a price on any specific legislation but calculates cost based on a 10-year waiting period, after which newly legalized immigrants could tap into federal, state and local benefits. A similar waiting period is included in the Senate's bipartisan legislative proposal now under consideration.

The findings quickly drew fire from advocates for illegal immigrants -- and also from a number of Republicans who have come to believe that the party must back citizenship for illegal immigrants or surrender the growing bloc of Hispanic voters to Democrats. In the 2012 presidential election, for instance, President Obama won 71 percent of the Hispanic vote compared to just 27 percent for GOP candidate Mitt Romney.

Shortly after Heritage released the study, former Mississippi Gov. Haley Barbour, who now works for the Bipartisan Policy Center, told reporters in a conference call he thought the Heritage study was political in nature and "warped."

The House's fiscal watchdog, Budget Committee Chairman Paul Ryan, R-Wis., also refused to back the Heritage report, suggesting it did not take into account potential economic benefits from expanding the workforce and tax base. "The Congressional Budget Office has found that fixing our broken immigration system could help our economy grow," Ryan said. "A proper accounting of immigration reform should take into account these dynamic effects."

The report was also panned by sponsors of the Senate immigration bill.

"Here we go again," tweeted Sen. Jeff Flake, R-Ariz. "New Heritage study claims huge cost for Immigration Reform. Ignores economic benefits. No dynamic scoring."

But the new president of Heritage, former Sen. Jim DeMint, R-S.C., argued that it is Flake and other backers of the bill who are wrong by not including a cost estimate beyond the 10-year window, when legalized immigrants will become eligible for many entitlements including Medicaid and health care.

"It's clear a number of people in Washington who might benefit from an amnesty, as well as a number of people in Congress, do not want to consider the cost," DeMint said.

He called the pattern of having the CBO provide only a 10-year cost estimate "their normal tricks," aimed at keeping true costs hidden.

The intraparty debate will play out at hearings in the House and Senate this week. The House will take up immigration reform in a series of bills, a move that DeMint endorses.

Cost is likely to play a major role in determining whether a path to citizenship can ever pass the Republican-led House. A key lawmaker negotiating the bill told The Washington Examiner the deal could "blow up" if the cost is high.