Agreed! I got a nice rock for my 5 gallon just in my back yard. XDDoesn't get any cheaper than free rocks/driftwood gathered from outdoors. That's where most of my tanks' decorations came from. Just make sure that any rocks/wood you collect are clean, have never been near pesticides/chemicals, and are a safe type to put in fish tanks. I found this article helpful: http://www.cichlid-forum.com/articles/rock_metals.php
Otherwise, I've heard of people getting cheap decorative rocks from garden/hardware stores. They're used for landscaping. Make sure they haven't been painted or treated with anything, of course.