If you get a corn/king/milk snake, this is the cost you're looking at:
say 60$ (possibly less) for the animal, 5$ for substrate, 10$ for a heat pad or basking lamp, 20$ for hides and branches and a water bowl, and 5$ for a regular 40W bulb for light. Allow an extra 30$ for other expenses. Not very expensive.
It'll cost a few dollars a week to feed... between 50 cents and 2$ a week depending on size. Plus paper towel and water.
They don't need UV light.
You can definitely handle a corn snake. Kings and milks tend to be more skittish but can be tamed.
You can give corns a nice set up with plants and bark mulch. Not desertic.
They don't need too high humidity, just spray a couple times a week. No biggie.