+1 for
https://sourceforge.net/projects/ard...?source=navbar
I've built 2 of these now, total cost with a geared stepper is around $120.
But..... you will need some basic experience in assembling circuitry and wiring.
Rob has an excellant 100 page manual for assembly and setup d/l here
https://sourceforge.net/projects/ard...2.pdf/download
If your are interested in building one I have a spare circuit board.
The focusers works flawlessly, best addition I've made to my setup.