Try ebay, here's one set of tires and rims for $300:
http://cgi.ebay.com/ebaymotors/ws/eBayISAP...sspagename=WD1V
There's also car-part.com which will let you know what the local junkyards have. Probably better than ebay as you can go down there and see what they actually have instead of just relying on pictures.