Hello and welcome.
I have been using EcoEarth, and it has been my favorite of substrates I've used, and it's only $7 for 3 blocks at Petsmart. That's ~21 liters of substrate, so I usually pay ~$28 for all of my substrate. I've used paper towels, ReptiBark, and EcoEarth and EcoEarth is the best. Maybe I didn't use the ReptiBark correctly, but I found maintaining humidity nigh impossible with it and it was quite harsh on my ball pythons belly and he often got little splinters from it. Most were really super tiny, so they might not have hurt too much, but they were big enough for me to notice and he had a few decent-sized ones. So, now I use EcoEarth a few inches deep instead. He never buries himself, but my boa does when he gets new bedding, he must like the smell or something. >.>
I agree with Lankyrob, if you don't think you could afford even just substrate, I would wait on getting it. If you already have it, think about whether or not you could afford a vet bill and decide if it's really the best time to have one right now. Vet visits aren't cheap, especially since snakes are exotic and you'll need a specialist vet. Not even just a regular exotics will work. I've met a few exotics who didn't know how to work on snakes, only mammals such as Guinea pigs and horses.