How to do it for under $100 INCLUDING A THERMOSTAT:
Hefty 100-qt tub, normally $20 currently on sale for $8 (I bought a dozen of these recently because they're just too useful and not just as snake tubs)
https://www.lowes.com/pd/Hefty-25-Ga...g-Lid/50150118
Depending on the size/brand you get, a UTH will run $17-25 from Amazon and a thermostat is $20-30. For $26 you can get one from iPower that has a thermostat/heat mat combo hard-wired together. It's not the best but if you're going cheap and you're only getting one ball python it's a lot better than an unregulated UTH.
Amazon has IR temperature guns from $4 to $40. Not sure I'd trust a $4 one but there are plenty in the $12-15 range that will work.
The AccuRite thermometer/hygrometer with probes is normally $12, currently on sale for $9.
Water bowls are available from the dollar stores for a buck apiece. Get two so you can swap them out when your snake uses it as a toilet.
Hides - Plastic food containers for microwave lunch/dinner meals are free after you've eaten the food in them. They also don't mold like those log hides do.
Substrate - newspaper is free. You can even make hides out of it.