Cheap Industrial Centrifugal Fans
 

I found a great source if you are searching for a centrifugal fan.

I needed 2000 cfm at .5 SP, the fan I found (2596 cfm at 0 SP - the best deal I found anywhere was nearly $900, I found this site (they manufacture it but it's not the official manufacturer's website). I found my fan for a little under $500. They appear to be top quality and are commercial models. They also had even thriftier downblast models, but my studio is 15 yards away from the back door of my neighbor and it would have added 7 Db to the noise factor.

www.ventilationdirect.com