Announced today, Amazon is now accepting used audio CDs through its trade-in program. In exchange for your used and unwanted CDs you will receive Amazon Gift Cards. Amazon's current program allows old electronic gadgets, textbooks, DVDs, and games to be turned in for gift cards. The program covers shipping costs.
The CDs are expected to be added to the program today, but it's not yet available on the Amazon website. Because of this, I am unable to say just how much money you will get for your CDs, but I can't expect it will be much. I would hope it's at least enough to get digital copies of half the tracks from the CD you sent in. More as it becomes available.