Check out this thread I wrote on AP cages: http://ball-pythons.net/forums/showt...With-Pictures!
You should be fine with just using the flexwatt sold by AP. Ap cages stay warmer than the room they are in, because the are so well insulated. You can use a on/off style thermostat, but I would recommend replacing it with a proportional thermostat when possible down the road.
Here are 2 good thermostat options:
Budget: http://www.amazon.com/Hydrofarm-MTPR.../dp/B000NZZG3S
High Quality Proportional: http://www.spyderrobotics.com/store/...4edb33b6438d7e