I posted a while ago here: http://www.teachat.com/viewtopic.php?f=36&t=16272&p=207437#p207437
asking a similar question.
There does not appear to be much interest in grinding your own powdered tea (from tencha or others,) and there doesn't seem to be much support for it in the industry.
Kyocera makes a small mill, however it's quite expensive for its parts, which amount to perhaps 5 dollars worth of material and they sell it for $60 and it might have to be shipped from japan.
Getting the most out of your tea requires grinding it, and I enjoy the extra flavors imparted by the more complete infusion.
I'm ultimately looking to spend $30, but I put a hard cap at $50. I think that should be completely reasonable for two tiny grinding stones, a hand crank, and casing.