The biggest obstacle for most people when replacing controllers is not having one that matches what's on the motor and bike. Sondors uses molded plugs, so you'll want a motor and accessories that match.
One can buy a motor/wheel with controller and accessories, that uses molded plugs, for $250. You probably cannot buy a stand alone motor, plus accessories ( brake levers, throttle, display and PAS sensor) to fit your Sondors for much less than that.