Hey Dave that exposed large pulley looks like it could drag you in and grind you up nicely too ! A cheap option for the large pulley would be one off the drum on a broken down front loading washing machine, not too sure how popular that type are stateside but they are the norm over here. They're usually fitted with a polyvee drive belt which would probably be happy running on a plain diameter drive shaft, which with the right sized bearings would save the cost of an intermediary pulley.
Most importantly you'll want to do the proper pulley/gearbox calculations so the grinder doesn't operate at more than 30-40 RPMs....any faster than that you're asking for trouble....smear...heat...etc.
With the gear reduction you shouldn't need a very hefty motor...1/4 hp maybe!?