My latest copy of Hemmings shows that model ranging from $1500 (rough, for parts) to $38,000 in like-new condition, fully restored and show condition..
From what you describe yours need a lot of work and has high mileage, and I would guess somewhere between $1500 and $4500 according to Hemmings. Don't count on getting any more. As others say, it's what someone is willing to pay.
I tried to help a friend sell his 1973 SL hardtop/convertible with only 80,000 miles on it in mint condition and maintained by the dealer. That car would fetch about $15,000-$18,000 since it needed no work.
On classic cars you are basically paying for the restoration work done by the seller, unless the car has exceptionally low mileage and no restoration is needed.
Hope this gives you some perspective.