ideally you want 5000 lumens per sqft. In a 2'x2' area that would be 20k lumens I believe

However if you could get about 5k lumens directly above/around the plant then I think that would work equally as well.. 2 plants = 10k lumens in lighting.

I wouldn't give up on the hps just yet..

Look into getting a 4" pyrex bake a round tube on ebay. About $15 shipped to your door. Then find the highest flow duct fan you can find (this is the cheap solution.. ideal solution would be an inline fan) and hook it up to one end of the cool tube with ducting. Leave the other end completely open to help draw out air from the inside of the room.

Be sure to place your exhaust as close to the top of the grow space as possible and place a passive intake or 2 down towards the bottom. Hot air rises and cool air tends to settle towards the ground.

Don't run an active intake unless you can match the same air flow as your exhaust fans. This will be more of a restriction than it would be helpful.