We need some people who have used CPU fans for exhaust to chime in. I think you are on the right track principally, but I dont think a small cpu fan is going to cut it. I don't think their CFM ratings apply to a large environment?? Not sure, but something is screaming at me that it won't be enough.

How about instead of investing in cooling, invest in CO2. It will allow you to run much higher ambient temps, especially if you go the LED route. It also won't cost nearly as much to run. Just another thought. You could keep the room sealed throughout lights on, and you could run a single exhaust with a carbon scrubber on a thermostat or timer. I don't run CO2, but I'm sure someone can chime in that does:thumbsup:

How about installing a backdraft stopper at the point where your A/C is going to enter the room. It's like a one way valve almost where the pressure from the a/c should open and close the vent as it goes on/off. Just throwing ideas out.