Check ebay. If anything worth selling is there click "watch this item" and see what it ends up selling for after the auction is done. Based on the number of bidders it can also show you how popular a specific item may be. Also go to other bike forums aimed at specific bikes and check their "for sale" sections.
I like ebay because quite often I can figure out if a certain part fits differant makes, models, and/or years and by knowing that and advertising it that way you reach more buyers and get a higher price.