Prices for C30s
You can check the blue book, as suggested, but let me give you a more labor-intensive way to check prices. Go through the sailing magazines, sailboat books (like Yacht trader) and newspapers for as long as you have to gather this data. Graph--literally take a piece of graph paper--and graph out the price of each boat you see. Use price on one axis and year vintage on the other. What you'll find is that things like installed equipment has virtually no value in the price of the boat (contrary to what the blue book says) but of course the more "stuff" you can get the better. I did this when I bought my C30, and way, way, way underpaid for it. I passed by several overpriced boats on the way ... boats that everyone told me were priced right. But priced right in your area may be different from the blue book. It's a pain but it works.