The Dollar Store has tons of kids puzzles. Not only are these great for hand-eye coordination, logic and just plain fun, but they're great to decorate with. And it doesn't cost anything more than the puzzle itself and a material most of you have at home!
Simply put together the puzzle (with your child's help of course!) Carefully lift and flip it over, pressing any pieces back together that slipped. Use masking tape to in strips across all of the seams, horizontally and vertically. Carefully lift it up and check to see if any pieces are slipping. If they are, secure with more masking tape.
Make masking tape loops to secure and press onto the wall. (I like to use masking tape to hang very light weight items because it doesn't leave holes all over your walls and it doesn't tear through paint and drywall.)
Cost for a cute decor item for your child's room? $1! Of course, you could always frame it or add embellishments, but really..you can't beat $1 for children's decor!