There are some nice drawing of how to make one yourself out there for the cost of a small 3/8" drive butterfly impact wrench. All you do is mount the air control valve remotely to get the fwd and reverse. A small air cylinder is wired in paralell with the air wrench and drives the air wrench, with appropriate socket, on the drawbar. Use a couple of springs to raise it off when not in action. It is the same way that the expensive ones work, just a whole lot cheaper. I picked up the wrench for less than $20 us and salvaged the rest of the stuff from the work dumstper. I have not made mine yet, but maybee next year.
I think there is a you tube video also.
You could also google diy power drawbar or something similar to see what comes up.
Mike
Warning: DIY CNC may cause extreme hair loss due to you pulling your hair out.