DL,
Welcome to the '65 GS Clubhouse.
The market value of any collector car is whatever the seller is willing to sell and what the buyer is willing to pay. That being said, the overall condition of a '65 GS convertible will be the biggest factor in determining the value. You ask for a driver quality with no rust. No rust is a big plus, especially for those buyers in the snowbelt. I checked with NADA for their numbers; low retail $13,750, average retail $19,665, high retail $33,695. I think that those numbers are fairly accurate. Are you a buyer or a seller? If you have photos to post of the exterior, interior, engine and undercarriage, that would be helpful. Whether you are a buyer or a seller, this forum is the place to ask. We are a small, friendly group of '65 GS fanatics who can assist with any specific questions.
John Egel