The best thing to do is hit the auction sites like Mecum and Jackson-Barrett. They will show what cars have sold for and then you can make a much more educated guess. Same goes for Ebay as well but make sure you look at the sold for price, not asking. Vette magazine would post what prices have been over the last couple of auctions, not sure if they still do that.
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Dave C..........My mantra: I can not be bought!! Long and short term leases available.
In the words of Zora Arkus-Duntov "Is your seat belt fastened? Alright, Let's go"
Yeah, I know, Shut up Dave.