I don't care much for the jailers, but what about the families of inmates who might want to visit them? Will they be forced to travel out of state? Couldn't denying someone visitors be construed as cruel and unusual punishment?
Think about it this way: in the days before motorised transport, were prisoners always kept within easy travelling distance of their relatives? I think not, and it wasn't cruel-and-unusual then.
For practical purposes, though, Montana to California is a bit too far. But Nevada spends only $20K, and there's not much of Calfornia which isn't within a reasonable daytrip of somewhere in Nevada.
Mexico probably spends even less, though contracting prisons out to Mexico might cause genuine constitutional issues...