The prison crowding solution is simple and cheap.
Set up a 640 acre escape-proof area in a moderately wooded area.
Put them in there.
Supply the needed electricity, water and sewer service. Drop food, guns, ammo, knives, axes, cigarettes in there by airplane.
Supply just enough food for 1800 calories / prisoner / day, enough cigarettes for half a pack / prisoner / day.
No guards, no roll calls, no supervision at all.
Let Darwin take over.
Don't forget to provide shovels so they can bury their dead.