I worked for a company in Portland back in the mid 90's that made a version of that. They had both inflatable and roto molded pontoons, but you sat more like in a recombant. It was super interesting, I think they were called sea-cycles. They weren't really marketed for the general public but were typically sold to resorts as rentals, seemingly a bunch in Florida and the Carribean. I never got to go on a service call. They were spendy but no where near $7k, maybe closer to $2K?
I'm pretty sure the last thing I'd want to do is sit way up on a tiny saddle in my boat. Looks like something for the masochist.
Yesterday's gone on down the river and you can't get it back. - Agustus McCrae