First off, where do you live? Down here in Fl I use no heat source and know many other people that provide no heat for their snakes and they do just fine. In the winter the coolest my house ever gets is 75 degrees and that's cold for me lol.
As a pet I would say most ball pythons can do well at or slightly above room temperature, just make sure they are digesting their food well and defecating regularly. Undertank heaters can be bought for glass aquariums that will keep it warmer too, the only problem with these is they don't stick well if you eventually change it to a new tank. I use regular heating pads(FIRE HAZARD>LOL) under my cages that are housing snakes I am trying to get to eat well all winter.
One good way to save $$$ is using a tupperware(I prefer sterilite brand) container instead of buying a glass aquarium. Just make sure the lid is secure. Also, paper towels or newspaper work great as a bedding. It's much cheaper than aspen or bark etc and is easy to clean, without the worries of snakes ingesting substrate when eating. Don't buy an expensove pet store water bowl made for reptiles, they may look nice but most don't hold much water and they are expensive, instead, buy a cheap plastic cat or dog bowl that has flared out sides so the snake cannot tip it. You can buy a hide box from a store, or you can make your own. I don't have 2 alike, but all are either small cardboard boxes with holes in them or gardening pot bases flipped upside down. One last way to save money is to find a rodent wholesaler to buy from. If you want to take the time to thaw out frozen rodents you can save big money doing this. Pet stores near me charge $1.60 and up for a mouse which was killing me until I found a wholesaler a few blocks from my home that allows me to come and pick up however many mice I need any day of the week so I can pre-kill and not have to freeze them.
Here's my cheap ball python formula(all prices are estimates)
1 Sterilite container of your size preference($3.00)
1 Newspaper(50 cents)
1 cat water bowl(1.49)
1 small box from around the house(FREE)
and if you like
1 general use heating pad($10.00)
You could easily get everything everything your snake needs and maybe even something for it to climb on for less than twenty dollars.
Just make sure you buy a good snake, a sick snake can get costly.
Good Luck with your decision, my first snake was a ball python I recieved as a gift 13 years ago and my interest in snakes has only grown stronger and stronger since.(R.I.P Mr. P)
Cole Maas