When an illegal gets caught for illegal
re-entry, that is entering a second time after being previously deported, they are charged with a felony and receive a year + in prison for it. That costs taxpayers millions upon millions every year. Many illegals send a big chunk of their money home where it spent outside the US.
https://nextbillion.net/immigrants-build-houses-in-mexico-with-remittances-the-case-of-c/
This pulls billions out of the US economy every year.
Worse for Americans is that illegals in the construction industry often do shoddy and dangerous work leaving your new home with serious quality issues. Seen that a lot personally. For example, when I find electrical tape on wire nuts, I know it's shoddy illegal work. The union guys and American workers would never do that, they know better.
I've seen electrical tape used to cover nicked wiring and wiring that was improperly stripped too, again illegals who don't know what they're doing.
As for what to do with them, I'd say detention camps where they are put into labor to raise the food they consume, etc., until deported. Also, the courts should take everything they own as the ill-gotten gains of criminal activity. Tack on making it illegal for them to conduct banking transactions and enter into contracts. They should not be able to get any sort of official ID like a driver's license either. Make it so they cannot function in US society and they'll leave of their own accord.
Also, start seriously prosecuting employers who hire them.