Looking at completed auctions on GB helps, also, open an account if you dont have one, and search and save all the similar guns on sale, and see where where they go. The ones that are too optimistically priced get no bids, Take the average. Some seem to slip through the cracks and sell fairly low-ish, some get bid up crazy high for some reason, but they rarely start high. Also, check out the Colt forum, maybe ask what difference the grips make, or get a set of correct grips and get it back to factory correct.