Have you gone through the phone book in the yellowpages under signs? A popular place is Sign-a-rama, but be carefule becasue each store can sell it at it's own price. I would also look for small, independtly owned stores, since they are usually cheaper and nicer to deal with. That's how I got mine for $10! Sometimes if you tell them that it's for a pig cage they go cheaper since they sometimes think you are trying to turn around and sell it yourself.
On the homepage there is a link for where to find stuff.
http://www.guineapigcages.com/where.htm
Good luck!
P.S., I saw your waffle block house and sent you a PM. Where did you get the materials for that, i love it!