You are looking at spending 10-15 USD, however not sure if it's cheaper over there. Noctua is the way to go. You don't only want quiet, but you also want quiet and move a lot of air, and that's where Noctua shines. You can have a fan that is super quiet, but not really effective. Or you can have a fan that is super effective, but not really quiet. Noctua finds the balance between both. Sometimes, I have to put my air to my case to make sure they are still spinning, but my temps are always cool. The only reason I could hear them is because I may have a fan curve to cool down my CPU when I am doing something intensive.
TL;DR - Get Noctua PWM fans and you will be happy.