I have had good luck with Sargeants, not so good luck with Corbin, but the really good seats have been Rich's and Sunmark's. All of their info is easy to find via Google. The prices range from about $300-$600 (but that is usually a gel pad and an entirely new cover, which is usually needed when the foam changes significantly).
See if you can find a local seat upholsterer, the type that does hotrod & airplane seats and convertible tops. When I had to recover a 550 zephyr seat a while back they were quick, reasonable, and offered various options in material & stitching.
I had a great experience with sending in a thrashed stock 919 seat to Sargent last year.
They added gel inserts front and rear, moved the rise forward and lowered the seat for my short legs, and recovered the seat in grippy vinyl for $270.