Not what you want to hear but I'd say around $4500, give or take.
Straightening out all that body work and paint the right way isnt going to be cheap and a prospective buyer will take that into consideration.
I would just keep the car because if you sell it, you are going to take a big hit.
In any case, if you do decide to sell it, make sure you fix the A/C, pinging-bucking and driveability issues first.