Looks like $19 shipped on ebay. I like the idea, but it looks like 5 or 10 min to make one, or wait a few months for the nicer final version to show up from this seller or somebody else.
While I won't rip the guys idea off for $19, what I can see happening is that I don't buy one because I don't see a need for it, then sometime down the line need one and spend the 10 min or so to make it and use right then.
What I can see trying is to make one using a cheap bar clamp instead of a threaded rod and nut.