Well, your description above certainly does change things a bit. I would move to the lower offer amount and work from there.
Again, IF the seats are in real good shape WITH tracks, that is something you don't have to deal with. A body buckets in driver quality with tracks can get pricey.
If you are planning a performance build at all, you will want to lose the 7 1/4 rear, for an upgrade. A body 8 3/4 rears set up appropriately can get pricey.
Floorboard, hmmm........ will/can you do that yourself? If not then there is added cost right there to get it done properly.
It really boils down to, how much work do you want to do? How much can you do yourself?
I'm sure you can do most of the stuff yourself with help if need be from others.