I rigged up a "Gilligan's Island" style exercise bike to grind grain. After a few minutes of turning that crank by hand, it did get a little tiresome, moving your arm in that big arc.
I would grind about 12 lbs at a time, and pedalling that bike was pretty easy.
I used a funnel made out of a cut out plastic laundry soap container, to keep the dust down.
I was looking to build a roller mill, when I dropped out of brewing back in 1993. I moved out of state, and lost my brewing space.
Thinking about starting up again...