There's a yellow and black Stanley blower that sells for about $45. It's 3 speed, 50/150/250 cfm. That is the most powerful low-priced air mover that I have found. I have seen it at Wal-Mart and Menards. It's a blower, and not a flush-mount fan, but it does a great job moving air. I have found that a lot of in-line ducting fans do not seem to deliver the advertised CFM rating at all.

Thanks Cole Robbie for chiming in! I'll certainly check it out! I've found a 10 x 10 fan (750 cfm) online, but it's $126.00!!!

This Broan 507 Chain Operated Utility Fan might help. ItâÂÂs pretty strong.

You can often locate a used fan at auctions for a reasonable price. For my 3 greenhouses (5 exhaust fans) I've never purchased a new fan and since I have backup replacements I probably never will. What you want to look for is a good accompanying louver that closes tight and opens well.

You likely can get by with a relatively small fan but you should also consider makeup air. Do you plan to prop a door open every morning before allowing the fan to operate? This also invokes the thought that you likely want the fan operated with a thermostat. Just some things to consider.