I'd say keep looking at the cheap 5 dollar foam planes for your project. The best quality foam glider I've found was sold at KayBee toys here in our mall, I bought out their stock of 3.

ALso...
If your looking for something a little less conventional. Look at Home Depot for Pink Foam and make flying wing's out of it. Just use 1 inch or 3.4 inch thick pink foam and shape the leading edge.
1/8 ply firewall, packing tape covering and balsa control surfaces...and away you go!!

Check out James Mack's page for some ideas!
http://www.jmack.net/html/rcmodels/combat/

Have fun!!
CrazyHerb