The suspension mechanism on those smoothride seats look just like the tractor seats which cost about $100.00 each. Glyde Ride seats are very similiar as well.
A couple years ago, I saw a boat where the guy took the tractor seat suspension mech and bolted a different seat to it. he said they worked great and for the price you can replace them 3 times for the price of the smoothride seat suspensions.

Here's a link to a page describing how one guy installed the tractor seat suspensions in his boat.

http://www.dwfonline.com/Articles/poor_mans_glyde_ryde_seats.htm


steve