If you have a dollar tree near you, they have some great room wall decorations that peel off later. also a great coat of paint does wonders for amy space. We just got marvel posters from there for 50 cents each for my son's room, and re-did the bathroom in a jungle theme using the wall stickers. Everything in there is a dollar or under, so maybe go and see what you like.
Also--go to freecycle.org and sign up for the local site. You can p/u great things others are getting rid of, and post "wants' for other stuff you dont see listed.
good luck!