If you're worried about lack of space and money in U.S. prisons, how about we:
1. Deport the 30% of the prison population that consists of illegal immigrants.
2. "Finalize" the 600+ inmates on death row in California.
That is a start. However, deporting does not seem to work as far as prisoners is concerned. Did you see the report about that guy that murdered that man and shot his son? He had been deported and then sneaked back in, had an Oregon driver's license, too. Now they are hunting him down.
However, that is a tiny drop in the bucket to our current prison population.