I buy used CDs sometimes .... though with shippung costs .. they usually come around to like 5 - 9 bucks a piece, unless i bid on like bulk lots on e$ay .. but then usually a bunch of the cds aro ones I already have, or are crap that I dont want.
Usually I buy new cds from places like redstreem, end records, southern lord, relapse, or dark symphonies ... CDs go for like 9 to 15 bucks at those places (with free shipping) And if Im looking for something out of print or hard to find, songsearch has an awesome selection (though prices are a bit steep)