Buy a copy of the Old Card Price Guide. They use current auction prices, and have a 1 thru 5 rating based on year, make, and model, 1 being junk, and 5 being pristeen. It's what I use to value my classic car occasionally for my stated value insurance policy. You don't need to buy a subscription if it's just for one inquiry... See the pic...

Do you have any pictures you could post. Might help people better when trying to guess a price.