I do have several options of drives available. but non are as cheap as a batterydrilldrive. Rather expensive compared to those even.
I can be contacted in several ways. PM, MSN or Email.

But for rpm. That is dictaded by wheel diamter and wished for speed. And speed is dictated by your motorpower, in the end.
Aim between 12-15km/h (8-10mph) for a drill based drive (faster is possible, but will eat amperes)
25 mph is no sweat for the high torque Speed 900s I regulary use.