If you just want something cheap, you can get a low RPM Top Motor fan from the same place for $3 ($1.50 for the sleave bearing version) that is only 24db. Their shipping rates are pretty good, but you might want to throw in a few more things like an SK-7 heatsink to go with that 80mm low RPM fan for $25.
PanaFlo does make an L1A 80mm fan that is only 21db, but they are pretty hard to find and tend to be pretty expensive. I used to run a pair of 92mm L1A fans in my old case. I got them from CaseEct, but they got baught up by Directron and this is their list of quiet fans here:
They have lots of fans including Zalman (20db), Panaflo (21db), Papst (12db), EverCool (25db), Vantec (21db), and Thermaltake (17db). They also have sound dampenning mats, silent power supplies, low noise heatsinks, speed controllers and even some of the best water cooling out there: