I was at Sports authority a couple of days ago and saw a small yellow sit-on-top kayak for sale, for around $120. It's smaller than anything I've ever seen in a store here before. At 6ft not quite as small as one of those tiny sit-in white water kayaks but small enough to make a reasonable float. With some dexterity an average size person could probably climb and sit on top of it, although I think it may be made for kids. But for sure you could pull half your body out of the water and rest on it.
There's not enough internal volume for storage if you were to put hatches in it, maybe small stuff. But the top has a nice depression and a bungee net and straps could be adapted easily for fish and gear storage. I'm sure it has a lot of flotation and reasonable drag. Anyways just an option for an almost ready float for someone willing to experiment. If I was shore diving more I'd go for it. When I remember the name of the yak I'll try to find and post a pic.