Don't get a zoo med rheostat, or any thermostat sold in a pet store, they are all overpriced junk. (Honestly you shouldn't go to a pet shop for advice, they very rarely have staffs that have even the faintest clue how to properly take care of reptiles)
Here are 3 good thermostats. I would recommend that you get the best one that you can afford as the thermostat is the only thing that will keep your BP from getting burned.
Budget: http://www.amazon.com/Hydrofarm-MTPR.../dp/B000NZZG3S
Mid-Range: http://www.reptilebasics.com/ranco-etc-111000-pre-wired
Best: http://spyderrobotics.com/home/products.html
This thread explains the differences between them: http://ball-pythons.net/forums/showt...t-Thermometers
I would recommend the herpstat 2 for your setup. The herpstat 2 will be able to independently control the flexwatt and radiant heat panel. (which MUST be regulated separately)