We have yet to do a retrofit on one of our Folding Fiberglass rear bench seats on any of the models, we have only done new installations. I believe the cost to add one onto a boat is $3500-4000 and a retrofit would be more as there needs to be some changes made to the boat to allow the seat to fit correctly. That being said, if you were looking for a regular rear bench seat, I would call Richie Wells at Gator Upholstery (954) 410-6544. He has done a number of them for our customers and the cost would be significantly less than the Fiberglass seat.