There are brushed and brushless DC motors. Depends on which one you want to control. Maybe you should look at jrkerr.com for the cheapest solution. They even do stepping styles. This will at least point you in the right direction for an engineering solution. If you want a ready made solution try SmartMotors (known as animatics). If you have a trivial problem try Anaheimautomation.com controllers. They also offer motors for cheap. I'm not sure how involved you want to get, but if you want to develop your own PID software maybe try looking at the BLDC kit offered by Luminary micro. Either way, you need to say what exactly youre trying to control and how dirty you want your hands to be.