For ONE snake and first snake, most of the cost is just upfront with buying all the equipment necessary. And then the cost of housing itself is literally nothing, just a bit on your electricity bill for the one heat pad, and one rodent a week for food. It's also much less cost if you use plastic tub setups vs. glass tank.
For my first tub setup for my first snake, upfront I paid about $150 total for thermostat, hygrometer, temp gun, heat pad, paper towels, water bowl, tongs, soldering iron (for holes in the tub), plastic tub, and plastic hides off reptilebasics.