So I built a box with some short legs because I wanted it at a low sitting height. Within that box I cut a circular hole, and mounted a replacement bathroom exhaust fan that I found for like $10. Around the fan goes another frame which I sealed real well with caulking.
I found a couple of small HV/AC air filters, a cheapo one to catch most of the crap and a very fine one that should handle most of the fine particulate. These go in the fame above the motor and are my filters.
Then another piece of ply to cover the whole assembly and I drilled a bunch of holes at the back where most of the dust is projected by the spinning buffs.
Built a rough hood (emphasis on rough, the duct tape truly does hold it all together) and mounted the motor on some 2x4 blocks to raise it up a little bit.
And here it lives next to my bench. The draw from the bathroom exhaust fan isn't terribly strong so I'm not sure how much dust it's pulling from the air, but I suppose it's better than nothing and the hood does a lot to catch most of the polishing compound that's flung from the buffing wheels. I think I spent around $100 in materials, far less than you would pay for any commercial polishing booth, and it fits my need pretty well.