From the world of m/c, a rule of thump is 80% of orig. bike price plus 50% of aftermarket parts. If you take the aftermarket parts off, you can often get 80% of aftermarket part price, so alot of sellers return the bike to stock and sell m/c and parts separately. Aftermarket parts on bicycles are not as expensive, but I think the rule of thumb is a good starting place. Some tricked out MX bikes have aftermarket parts worth more than the stock m/c.