Pricing a car like yours is somewhat subjective. A lot depends on the potential buyer. Is this the kind of car they have been looking for or do they like the body style. I have seen some very nice mid 70s lemans and GTOs.
In the shape yours is in, I honestly wouldn't expect a whole lot of money because the expense required to get it back in nice shape will be more than the value of the car, thus the subjective part. When you like a car, you fix it up for yourself, not expecting to get your money back.