What model is it? A Cutlass, 442, etc?
NADA online gives pricing for some classic cars and I got some fair prices from it for my group of cars. When I used it I did not have to pay, register, or anything. Just make sure you choose the classics or collectible catagory.
You would have to judge for yourself what "grade" it is in. The site will help you decide what it should be. This should at least get the ballpark in view...
It is nice it is up the street so you can revisit it often and convince yourself to buy it!

The wife and kids would love it.
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-Rob Young
1972 Cutlass Supreme Convertible (442 clone) -"Lady" (My mistress...)
http://www.flickr.com/photos/robsalbum/sets/
1986 Cutlass Supreme Coupe - "Pristine"
1978 Ford (Old Faithful) a.k.a. "the Tramp"
1997 Cadillac STS (for sale - too many cars!)
1999 Harley Davidson Sportster - "the Freedom Machine"