Hi guys you might want to have a look at these as a cheap alternative .
http://www.kineoptics.com/HC-2.html
$80.00 US bucks
There a helical crayford design , in that you turn the focuser tube to wind it in and out.
It uses a crayford bearing set up which allows for a faster screw motion than normal helical threads.
I actually got this given to me , and was going to get a Starlight instuments feather touch focuser as they use a Stainless steel tube so you don't wear grooves in them from the bearing , but have not seen the need with this unit .
You will have to be aware of the mounting distances though. , but that is easaly fixed.
The Kine handles a powermate and 30mm 80deg 2"eyepiece weight.
Mark