If you're cheap (or thrifty) like I am, you could try making your own. I think one of the magazines a while back had plans for one, based around a piece of 3/8"-16 NC piece of all thread. The 16 threads per inch give you 1/16 advance per turn, or 1/64" per quarter turn.
Plus, it's always fun to make something that costs "real" money, and spend your savings on something else.
Plus, it's always fun to make something that costs "real" money, and spend your savings on something else.