good post River Country!
You can certainly build one for far less. I would not use a bench grinder. I looked up my motor one time, and I think it was like forty bucks. I think it's pushing 1770 rpm's? It's a small motor. I have a switch as well, and it sits in a wood box with a plexiglas removable top on it, that I mount a light over. I bought mine from Rinehart taxidermy, and they cost like 400 bucks now. I would build one again if I ever had to replace it, but at this point I have everything there, and the only thing that would ever need replacing would be the motor. I would build the box out of a drum or plastic for darn sure for easier clean up. Mine is oak, which I line with paper before fleshing. Then I simply remove the paper and duck butter in one fell swoop.
I suggest getting a motor fast enough to take off fat, and small enough to stop with your hand. The thing to remember is the membrane is normally what will wrap around the shaft. If you start at the head, and flesh to the tail, you are removing those chances of strands by using this method. Pat Pitt is the guy who made this point, I tried it, and it worked great. Now it's the way I do it, and I am spreading the word. If the skin gets wrapped up, let it go, don't panic! Turn off the switch, and normally it doesn't do any damage. The problem is when you try to hold it from leaving your hands. My shaft has a cover over it, but there is still 3/4 of an inch that has a spinning shaft showing. This is where the nut tightens the wheel to the shaft. It will still grab a bird from your hands, if your are not careful.
I do think that if you are going to make the plunge, and invest in one single tool, that this is the one (unfortunately the first one) that is a must in my opinion. This fleshing can be the single most difficult thing about processing the bird. You might find you get discouraged quick, if you don't have the equipment to do it easier?