Cheap modelmaking supplies

Have you ever gotten sticker shock from modelmaking and terrain materials? I certainly have. But here's a tip you may not know: the art and architecture departments at your local university toss out a bunch of useable materials when the school year's over (i.e. right now). Styrene sheets, balsa sheets, heavy card, stuff like that. They make models, too! Checking out their dumpsters every so often can net you some good finds.