You could put down a cheap plastic tablecloth or shower curtain under the cage.
I bought some fleece (not fake fur!) and use binder clips from the Dollar Tree to fasten it around the back of the cage to protect the wall. Then I cut a 12" strip to wrap around the lower part of the cage so my dog can't get too close. I also covered the side closest to the AC vent so they won't get a draft.
Sometimes Walmart has thin fleece throws for $2.88 if you don't want to go to the fabric store.