You want the max bang for your buck. Just getting something that will move air is asking for a lot of noise and questionable MTBF. I had a Cougar Vortex 120mm hold up for 3 years then the bearing gave out due to contamination. It was a fluke. The rest run just fine and are real quiet. If you get just anything cheap, you're going to get cheap results.
Shopping for fans is as important as shopping for a power supply. There's a lot of junk out there.