The question should not be 'what is the cheapest setup?'....it should be 'what is the best setup?' If you cut corners with the enclosure, then you will most likely have to pay more down the road for vet bills.

Don't get any animal unless you can afford to take care of it properly.

Other than that little spill..... hockeyfan's list sounds pretty good....although depending on the temperatures inside the room you may need a secondary heat source(figure another $20). Also, with any UTH a thermostat is always recommended($40 min).

After all of that you should have a pretty decent setup. Now when you start looking around for ball pythons cheapest is usually not good. So shop around. I speak from experience when i say that it sucks when you spend alot of money on an enclosure but your ball python dies 3 days later because the seller that you got it from was selling sick animals at a cheap price to get rid of them.