Check my numbers

Approximately 25% of Federal prisoners are foreign born.

Of the 187,855 inmates in Bureau of Prisons’ (BOP) custody, 42,034 — or 22 percent — are foreign-born aliens, according to DHS figures.

And that's followed up with:

The average annual cost of incarcerating a single federal prisoner is about $32,000, according to a BOP report.

So 42,034 prisoners at $32,000 a year is $1,345,088,000.  Is that about right?

Send those fuckers back.  Hell, fly them back and kick them out of a plane without a parachute.  That'll save on costs both ways.  It doesn't matter if it's on the ground or not.