I did my own for less than $200.
On this board, I've seen guys say they got a shop to do it anywhere from $500 to $1400. It depends on the shop, and what time of the year it is. If you take it to a shop at the beginning of summer (when everyone else wants their boat done) expect to pay a premium. If you take the seats while it's cold... and the shop is slow... you will get a better price.
Sorry I can't give you a real price. You need to find a shop in your area, and ask.