What is the typical cost to have a ball python for pet?

1 snake to 1 cat????? I almost couldn't imagine

Overall, IF you get the snake set up correctly and the habitat right, There will be a bigger initial investment in the Ball python. I have had cats my whole life, and I think you generally don't need to spend a whole lot of money on, well, "stuff". You can if you want, but that is more for the human really. A cat can be made very happy as long as you love, play with, & take care of it. The old joke, "My cats favorite toy is an old piece of string." There isn't allot of need to buy new things, feeding dishes, litter pan, maybe a scratching post if you don't have something around already for the cat to use. (For example, I have an old wooden stool, I keep it just for the cats. I catnip it, and they are used to it, and that is their scratching post.) With a snake there will be greater initial cost.

But, as for regular maintenance, if both are taken care of properly, the cat will be more expensive. Food daily, litter regularly, that is more there in and of itself. If you live in an area where you need flea meds, add that. Any vaccinations. Vet visits. Random stuff like catnip. That list could go on, and that is just the basics.

Snake, a rodent a week, every two weeks for an adult. You can spend stupid money on substrates at a pet shop, but I find that to be foolish, and even then, if you spot clean, you still only need to completely change it every month at most, and that is erring on the side of caution, (which isn't necessarily a bad idea.) There is allot of other stuff people will try to sell you at pet shops, but most of it is frivilous junk.

All of this is ASSUMING YOU HAVE THE ENVIRONMENT SET UP PROPERLY. If it is too cold &/or too wet for extended periods, you will almost definitely have respiratory infections. If you don't clean the cage, you have a much higher risk of internal parasites. If you feed live, you have a higher risk of parasites, and if you feed live by just dumping it in and leaving it, you run the risk of it getting bitten. But all of that is controllable.