"Twist" from Sam's club is a whole lot more affordable
The Twist seems to be popular: http://www.paddling.net/Reviews/showRev ... l?prod=951
, but keep in mind the people posting these reviews are probably beginners. If you can look around for a used one by a brand name company, that might be a good call as well. My first kayak was a Dagger Cayman I bought at a garage sale for $200 including seat and paddle. Used it for three years before I got the Hobie, someone is still using it today.
He is not physically impaired except that he tires quickly and he cannot balance well enough to ride a bike.
We take a lot of people who may not be Olympic-caliber athletes, as well as a lot of little kids surfing and paddling in the ocean. At first, most are a little sketched, but get over it quickly. Learning to maintain their balance on a constantly changing platform(the ocean) is a good skill to learn. Being on the water is so much fun to them, especially the kids, they will put in extra effort to get the hang of it.