I have one of the Corsair budget quiet cases under my desk. I can attest that it has excellent bang for the buck, for being a basic black case with useful soundproofing/absorption.

As far as noise reduction for CPU cooling, I'd suggest buying more air cooling than you need for a modest TDP CPU. Between that and my fanless Seasonic power supply, and SSD, the only noiseI can ever hear from my machines is from the GPU.