What it's worth depends on its condition, originality, and how much you want it. I hear this question constantly. I ask myself this question constantly. Asking prices in want ads are generally optomistic. Selling price on eBay is often a closer indicator, but often reflects the desire of an individual, not the market.
If you're buying, compare and go with what you feel comfortable paying. As long as it is within your budget, don't worry if you "got a deal", buy the bike because it gives you pleasure in one form or another.
If your selling, this is tougher. If you need the money, be prepared to sell for less than what you think it is worth. If you just need the space, take your time, advertise widely, and wait.