Before you run off to Harbor Freight check out these guys on Ebay. These wheels last and last and they are well not cheap, but inexpensive. I buy a lot of them and they work great.
http://www.ebay.com/itm/270664732513?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT
http://www.ebay.com/itm/270664732513?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT