It all depends on the tubing the bike is made from. I have a Bridgestone MB-6 from the late 80s. I love this bike. Fairly lightweight made frome Tange MTB tubing. Bikes like this are quite commonplace and the frame would probably go for the price range you are talking about. That is quite a good deal considering the quality you are talking about.
However, if you are talking about steel frames made from Tange Prestige, much lighter weight with the same strength and stiffness, the bikes go for much more. The bikes would be like Bridgestone MB-1s, Specialized Stumpjumpers, and Univega Alpinas. These bikes are not quite so commonplace. I would love to have one but I can't quite justify the $400 to $500 and even higher prices that they often get. Overall the the price has to do much more with supply and demand than the increase in quality.
Also responding to T-mar. My MB-6 was ridden hard for many years before I bought it. I have ridden it hard for almost 10 years. I can't see buying this frame any more riskier than buying a quality old road frame. It is good to go for many more years the same way a quality road frame would be. It just happens to be a little bit heavier than Tange Prestige or Reynolds 531.
Last edited by russdog63; 01-31-07 at 09:06 PM.