I'm sorry but since when did a 4 inch or even larger can-fan cost 300 bucks?My guess is that a $300 can fan is a little overkill for this guy's grow.
Look, you can listen to the guys who hack shit together and end up with various results, you can try to build your own this and that our you can shell out the money, do it right, have no problems and never bitch. It really is that simple. A 4" can-fan pulls something like 68 watts and moves 150ish CFM. Do the math. Listen to the hacks, attempt their hacks and you will end up with the same low rent results. You have people with no experience tell you LED's are great, they are not. You have people say they get this and that with CFL's or Flouro, they don't. I wish there really was some magical cheap means of doing things right, but there is not.