I know this has been said about a dozen times now, but don't offer any more than $150, and even that's pushing it.
It's not that hard to find frame that fit, if you know where to look. 48-51cm frames typically go for less on eBay than a comparable frame of a larger size, because there's just a smaller pool of potential buyers, so you can start by looking there. Or, as others have suggested, just buy a 49 from Bikes Direct and be done with it.