One of the re-occurring questions on this forum is "What is it worth"? It's a difficult question for the newcomer (and possibly even the more experienced members?) .
Sheldon Brown started a rough price guide back in 1997 and while it hasn't been kept up to date, it has some good information especially with respect to the dynamics of price variability.
[Edit: Michael Kone wrote the original article for and Sheldon Brown put it on the web]
There's also good data to be mined on eBay, but past auctions are only visible for a short time and prices can fluctuate with time of the year.
Searching the web, one can stumble on pages like the following one that has a list of used bikes with prices at which each sold back in 2000-2002.
Another way of valuing is to look at the cost to build or get the same thing new, but this has no meaning when it comes to museum pieces. However, I think for the most part, a lot the bikes discussed here while perhaps collectible, are also ridden rather than framed.
Of course the perceived value can differ based on the perspective of the buyer versus the seller. When I sell, it's worth a lot. When I buy, it's not worth quite so much.
Anyhow, it seems a market is best at deciding the price. Is there anyway to look at older auctions on eBay? Or any general thoughts on price guidelines for used bicycles?