I too don't see how you're going to get a steal on used frames on eBay.

For my latest build, I've bought new things through eBay (Avid BB7 Disc brake, bulk cables and housing) and one old thing (pair of minimally used Nokians for about 75% of the usual advertised price). Unless it's going to be a big ticket item and there's a chance to be a lower price on an eBay store (like the Disc Brake) I just get stuff through Nashbar.