It's worth whatever someone is willing to pay you for it. There's bunch of them on this site http://www.corvairforum.com/forum/ that are selling for less than $5000
Your question is incomplete...there were 4 models of 1965 Corvairs and 2 to 3 body styles in each model. Corvairs have never sold for big dollars but some models sell pretty well. The condition is also a big factor. A Corsa coupe with turbo engine will sell for maybe twice as much as a similar condition 500 coupe. You can look online but sometimes the high asking price cars are just there to test the market.
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