I've had the best luck buying used CDs from Amazon.com marketplace sellers (there are hundreds of them, perhaps thousands, so it's a huge marketplace, and Amazon.com stands behind and guarantees your purchase). I've bought a great many CDs this way over the past three years and found it very efficient (saves a lot of time and running around) as well as highly cost-effective.
Source for low cost redbook CDs
I'm looking for any recommendations for good sources of CDs with a large inventory of music and reasonable or low purchase/shipping costs. Currently a member of www.yourmusic.com which offers a shipped CD for only $6, which seems to be the best I've found to date. Only problem is that they've got a somewhat limited inventory. I enjoy a wide variety of music - classical, alternative, christian, old and new rock etc. Any suggestions?