Not a boat, but I just had my 51 Chevy Truck seats done by a local guy who does a combination of auto and marine re-upholstery
He uses marine grade vinyl either way.
So just to give you some idea of some pricing .....
The bench seat below was $750 which I would say was an absolute steal.
That included a new cover over the springs (a sort or Scothbrite type of pad vs the original burlap) and the foam and material plus the manufacture and installation of them on the seat frames (I pulled the seats from the truck and just dropped them off)
He also made my full-height door panels (see the original pic where they are only about 12" tall, essentially just the area where the handles are), which included making the 22ga steel panels and then covering similarly to the seats - for $250 the pair!
I was able to pick from hundreds of fabric options and I designed the layout I wanted with the pleats.
He was kinda funny when I first called - he said bench seat and back $750 - I said I wanted a specific layout with the pleats etc and he said, doesn't matter, whatever design you want, it's $750
I'm in the Pacific NW (Seattle area) and I would think it might be lower cost down your way; but again it depends on what/who you can find. My guy was a solo operation and you might have better luck with someone similar, alhough correspondingly their wait list might be longer.
Don't forget to check with auto-upholstery shops - even if they don't typically specialize in Marine, they would likely consider I expect.
So you just need to shop around and find a local house and see what kind of estimates you get. As noted above, this time of year is also likely to have a fair extended lead time, wherever you find (and if they don't they may not be worth using!

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Incidentally I was going for 'old baseball glove' look. I initially asked him about leather and he wouldn't even entertain it. Convinced me over phone that the modern vinyls were so much better and whan I saw the pattern books I was doubly convinced. Actually, even my Mercedes does not have real leather and most are hard pushed to recognize that it's not.