New seat assemblies are expensive... we sold some a few weeks ago, I can't remember the exact numbers but they were roughly
Seat Bottom Assy: 180
Seat Back Ass: 110
Now that includes hinges, armrests, rubber dampners, screws, and for the seat back, screws, plastic backing cover.
Just for a rough idea of value anyway. The seat I mentioned above would go for about 75 HRC, so if you have a nice one... I'd say 100 or your choice.
Anyway.. I don't wanna step on any toes, Cost varies by so much on those. I just wanted to offer some idea of what they can run