I used to run my 400watt in a 2'x2'x5'6" area with a crappy batwing reflector I got for like $30. The way to keep things cool is to buy a quality fan. Well, it doesn't even really need to be quality, it just needs to be made for what you are using it for.
You can get a cheap 465cfm blower on ebay for like $100. You can go down to the next size, but its only like $20 cheaper and the 465cfm one will do a way better job, plus if you upgrade to a 600watt, you can still use the same fan.
Those duct booster fans do not do a very good job as an exhaust fan. Sure they are like $50, but for another $50, you can get something that will work. Those booster fans lose like 80% of their cfm going through a duct run. I have one that is 420 free air cfm for my a/c light and after a 5' duct run, my 130cfm computer fan I have for an intake blows more air. Don't waste your money on a booster fan.
When I had my 400watt light in a 3'x2'x6' cab, with the 465cfm fan, my temps were only like 4 degrees above ambient temps. This means that I could keep my thermostat at like 78degrees and my plants were fine at 82degrees. You may think you are "saving" money buying a cheaper fan. But $50 extra on a fan is a lot less than a $200 electric bill every month trying to keep you room cool.
In the beginning I tried to pinch pennies here, buy the cheaper of this and that. After a while you figure out that the cheapest is not what works best. Sure, you don't need to pay for a brand name, but you need to correct equipment. Trust me, you will be happy you spent a little extra when harvest time comes around.
