I think I may have found my chair:
It's a bit weird, with only two legs, but it rocks (in the forward and back sense, not the headbanging, "dude, this band rocks!" sense), it folds up very small, and it's reasonably light at 18 ounces. And, the cost isn't too bad, at about $60.
I've ordered one and I'll post a review when I've had a chance to try it out.