RE: COMET Goldberg Sailplane kit
Max,
Collector kits are kind of a funny animal: You really never know what you'll get, though the Sailplane should fetch a good price. As far as what to start at, here's what "New" Sailplanes cost: The Midway Model Co. sells a partial kit for $139 and a full kit for $199. Bob Holman offers a laser cut shot kit for $80.00. But remember, the people who are after your kit won't build it, so there is a difference. Hope this gives you some direction!
Chuck