You're looking to buy the whole airplane, not the pieces.
When I buy a used car, I pay what the car is worth, not what the individual pieces are worth.
It sounds like the seller wants it both ways - you pay for the pieces, but he doesn't have to go through the work of actually parting it out and storing it while finding individual buyers.
I wonder if you can get an estimate from a salvage yard of what they would pay for the whole carcass, and then offer the seller that amount.
