Cheapish 140mm silent case fans?

I am building a computer with the Fractal Design R4 and i want to add more case fans so i can keep it cool but i also want the fans to be silent or quiet.

Just get another 140mm Silent series R2 fan and run it at 7v with the integrated fan controller, should be whisper quiet and still move a good ammount of air.

ok thanks i was thinking that and those are pretty cheap but i was just thinking there might be something better.