I bought a 50/1.4 ai in nearly mint condition for $50 a couple of months ago, then picked up the hood for another $14, locally, so I guess I did OK.
The secret, I think, is to look for things people don't bid on because the info is inadequate--in this auction the hood obscures what's under it. My lens had only one blurry photo, of the underside of the barrel, and said nothing about focal length or speed--I just happened to recognize the 50/1.4 proportions, and trusted that the filter it had on it meant the person who owned it cared enough to take care of it. I recently picked up a clean 55mm micro for the same price, and similar situation, and an insufficiently-described N90 for around $25. No other bidders on any of these.