Hi hoodie,
Both posts above are correct....however....
A case with lots of fans comes with lots of noise...i'm a gamer myself and have 3 case fans, and probably one of the coolest computers there is...it's not about fans, it's about airflow.
With the budget....you do need one, otherwise the cost of the computer will get out of control. But the most important thing in any PC - especially gaming - is your Power Supply (
PSU). This is the first thing you need to find, as if you get a no named brand, it can alter the whole computers performance.
I'd recommend getting a SilverStone, ThermalTake, Enermax or Antec...Antec being last on the list.