The Inland Empire's Daily Bulletin has a report on the recent CIS study that found that illegal immigration costs the U.S. $10 billion per year and legalizing those illegal immigrants would cost $29 billion per year. A Cato Institute economist tries to offer a talking point, but, thankfully, the Daily Bulletin lets CIS respond. From "Study: Illegal immigrants cost billions":

Some experts questioned the findings.

"Take this study with a grain of salt," said Stephen Moore, an economist with the Cato Institute in Washington, D.C. "This contradicts what most other studies have shown, which is that immigrants help the economy. Overall, they use less government services than they pay in taxes."

Moore pointed to a 1997 National Research Council report that shows the typical immigrant and his or her children pay an estimated $80,000 more in taxes than they will receive in federal, state and local benefits during their lifetimes.

Camarota said that conclusion is misleading because the report included legal and illegal immigrants and projected the earnings of an immigrant family more than 300 years...

It also includes some lovely quotes from a [presumably illegal alien] day laborer:

"We contribute more to the economy than the Americans who were born in this country... We do all the heavy work because the Americans don't like to do it... If all the immigrants got together and decided not to work for two days, the economy of this country would fall apart."

I'd imagine there are quite a few American citizens who would disagree.

The day laborer also said he himself wasn't a user of public services. However, not only is that false - you can't live here without using a multitude of public services - but any attempt to generalize from that would also be faulty logic.