the intake needs to be drawing in at least the same amount of air as is being pulled out by the exhaust.
You could always make a passive intake untill you can get another fan. Also like Hazeus said CFLs dont put off much heat at all so you want them close to the plants as possible. If you add more light then they will grow faster. After I added 2 cfls to my cab I saw a big diffrence. They sell Y shaped splitter things where you can have 2 cfls in the place of one.