I've seen those seats (67-68) sell here on the board anywhere from$200 to $350 needing to be recovered, on e-bay they usually go higher and if you count the shipping add another 60 to 100 bucks depending where you get them at, but since you can get those locally and you say they need recovered, offer him maybe $200 and go from there.
I saw a nicely reupholstered set at Carlisle last swapmeet and the were marked $1,350
I'd be interested on them myself if you don't want them and the price is right.