I saw some others have had a go at putting together their own arduino driven focusers, so I've had a go with some success. Total price is probably under $100 and is mostly the stepper motor.
This is the one I built:
https://sourceforge.net/projects/ard...controllerpro/
I used the recommended configuration and had it up and running with almost no problems. Only thing is the stepper motor did get very hot, but I think that means I need to play with the DRV8825 board potentiometer to get the current right.
The actual stepper motor mount is one I modified from another design in Blender and 3D printed in ABS. It's for a Skywatcher 200P with the Nema17-PG27 stepper motor, and the design can be found on thingiverse.
So now I can control the whole setup from inside my house - nice. I'd highly recommend people give it a go if they want to save a bit of cash versus a commercial product, though factor in a reasonable amount of time to collect all the components and to put it together.