Costs associated with illegal immigration aren't really all that clear cut, from what I've seen. Undocumented immigrants generate a lot of revenue and economic activity and pay a lot in taxes while not being able to use most government services.

The major drag on revenues that I was able to find is on state/local governments that fund education for undocumented children, which should probably be remedied with more federal funding to offset.

Tons of datapoints cited at the Wikipedia page on the subject