Looking for robot motor control

[eovnu87435ds]

the output gear is hollow, so a potentiometer can easily fit from the other side. It should take all of 10 minutes to do so. Then I just use EPA to limit it to where it will not over steer. The speed controller is accurate enough to consistently bring the motor to the desired angle and back to center many times over. I just don't happen to have $70 to spend on a speed controller. And unless I get high amp limit switches (~$25 a piece) and wire them in series normally closed to the motor wire. even then, there is nothing that would bring it back into operating range