Cabela's offering from Hobie...
The Hobie Float Cat 75 Expedition Package has molded, seamless hollow polyethylene (a plastic) hulls, and is supposed to be relatively durable. It is only 4 feet wide by 6 foot 3 inches long, so is on the small and short side. The whole package is supposed to weigh 33 lbs., and has a weight capacity of 350 lbs. Price is listed as $725. I don't know if the frame is steel or aluminum (or other) - it wasn't specified.
I am considering one for lake fishing (on calm days only) during the late fall/early winter. I can throw it in the back of my pickup fully assembled, and be set to go when I get there. I don't know if it could be used for rivers or not, but I wouldn't use it for anything but a fairly gentle run - no real rapids, as I would question its stability due to its small "footprint".