All a temp ban does is tell the cheater to hide it better.
Perm ban with the ability to appeal seems the logical route if you dont want cheaters on the server.
Admins can also add a one time only $10 (generic price, can be set to whatever) "unban me" option in the shop. If they have REALLY learned their lesson, want to change, and want to be productive members of the community, they can pay a small fee and continue to be part of this community... if not, let them rot on the ban list.