They don't cost very much at all once you get the cage and the snake. A bts would be much more expensive with the 50$ uv lamps every six months and all of the veggies. Not saying you shouldn't get one, I've heard they're great pets, but they are much more expensive.

Hydrofarms aren't that accurate (+-1-2°f), but unless you're heating an incubator they're fine. I have one for my leos and it's pretty reliable.

A heat pad for a ball python uses so little electriciy that it shouldn't make a difference of more than a couple dollars max.