Depends on a lot of things you haven't mentioned - is the drive train original and numbers matching? Might not be such a big deal with a six banger and a 3 speed, but it still adds value. Was the body work done by a restoration bodyshop, or just scabbed in? How's the rest of the body? When the floor pans go, there is usually more rust in other places. I would guess anywhere between $4000-10000, depending on overall condition.