I don't know about bargin priced, but there are several sources out there. I just ordered 10 belts and a MG3 feedtray from http://www.dsarms.com it's under their miscellaneous parts section. THe belts were used and $5.00 per section (50 rounds), the feed tray was $29.00 or so.
Robert rtg also has cans and belts, and the prices are decent, do a search for him in yahoo, he's the first link that pops up if you search robert rtg.
Other sources potentially for belts are: interordnance, marstar, northridge international, and ima.