Do separate autofocus motors exist for entry level Nikon DSLRs?

I have a Nikon D3200, which doesn't have an autofocus motor. Therefore, I'm mostly deterred by lenses that don't have focus motors in them. But the ones that do have it are much more expensive.

Take the Nikon 70-300 for example:

AF Zoom-Nikkor 70-300mm f/4-5.6G: $172.95
AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED: $589.95

So is it possible to have an autofocus motor as a separate attachment to the camera? This would go between the camera and the lens, like an extender. I think it should be doable in principle, but not sure if anyone makes them..