i got a 1200cfm squirrel cage blower from "the squirrel cage store" on ebay for like $80. this guy remanufactures (or cleans up?) used motors/blowers and will wire them however you want them. like i said, a squirrel cage blower is going to lose pull fast if there is a lot of restriction. it's not the best, but it still works. if you use furnace filters (the high efficiency super-small micron filters are the only ones that will work decently, and they take a lot of maintenance, or else the powder loads up on the filters, the pressure difference rises, and the powder pulls through blowing it all over your shop) make sure you maximize the filter surface area so the blower isn't trying to suck through a little opening. we used two (it ended up being four ...two stacked) 20x25" filters.
also, if you use a cyclone and absolutely need to exhaust back into your shop, you can add a post-filter to the exhaust. there are loads of info on these websites that will give you lots of good ideas.
http://billpentz.com//woodworking/cyclone/index.cfm
http://www.clearvuecyclones.com/