Ebay prices have a lot to do with who is looking for that kit, that week. If two or more bidders want it bad enough, there is no such thing as book value. Some kits consistently bid high, but even those have a bad week sometimes. And that's when I get them. I've bid up to $75 on a kit, lost out to higher bids a half dozen times on the same kit, and then won one for $30 or so the next time; and often a nicer one at that. It just depends who you are bidding against and how bad they want it.
-MJS