If you're look for cheap bedding, from my experience Aspen is the way to go. I can get a giant bag of it for $12 and have it last 6 months, while changing a rat cage, 2 snake habitats, and the mice house.

If you're looking for non wood you can try Yesterday's New, which is recycled newspaper pellets, or Carefresh which I think is also a paper/fiber type product. Some rats and mites get the sniffles/sneezing around Carefresh. I haven't had any experience with Yesterday's News, I just know it's another alternative.