Best bet is to get some good pics and post them in the 'how much is my xyz worth' thread. Hopefully you'll get some feedback. You can also search the site for previous sales using the search function above, or even use google with the keywords, Cannondale, for sale, retrobike. That should give you some ballpark figures to work with, failing that sell it for what you'd be happy to let it go for, that way you'll not regret it and if the buyer gets it cheap you'll have two happy people.