I make the cavy cozies from the instructions that I found on this website. I don't sew but can make two of these within 15 minutes. The only problem is that my two girls like to lay in them and pee and poop in them so I end up throwing them out. I pick up remnants from sewing stores or Wal-Mart to make them. I usually get like a lambs wools or fake fur for the inside and whatever material for the outside.
I also will use a small cardboard box big enough for both of them to fit in and just cut a hole so that they can get in out. I bring home from work empty toilet paper rolls that are like 4-5 inches big and put them in their cage to crawl through or chew on.
I try not to spend a lot of money on pet store stuff and try to recycle stuff in the house. I noticed that they sell at the petstore shredded paper but I use the shredded paper out of my paper shredder as long as it doesn't have colored inked paper or carbon paper. My daughter had a baseball that was new and I put that in their for them to nudge around.
I hope this is helpful but I don't think you need to spend the money at a pet store.