CONTINUOUSWAVE

Is $350 [a fair price for] a used Reversible Pilot Seat whose cushions need to be redone?

Talk to Tena @ Anderson's for cushion prices.
Note the RPS legs attach to the seat cushion (plywood base).
http://www.amfg.us

The Teak RPS is pretty pricey to replace. Does it include the rod holders and the grab handles?

The handles can be replaced - https://www.perko.com/catalog/deck_hardware/721/handle/

A complete RPS (legs, swing arms, mounting blocks, seat base and seatback with rod holders and handles) in good shape run $500 to $1,000.

HEAT’: Please read

viewtopic.php?f=1&t=3844

For advice on replacement of upholstered items see the list of recommended vendors in the REFERENCE section.

http://continuouswave.com/whaler/reference/OEM.html