used CD store

Most used CD stores also sell new CDs, if you must have the latest Backstreet Boys release right away.

The best part of the used CD store experience is the bargain bin. CDs that don't sell well are discounted, first to $5, then to $2.50, then to $1.00. If they don't sell at $1.00, they go into the black sticker section (at least at CD Exchange they do). 15¢ each, or 10 for a dollar. I like to go in periodically and scan these racks for interesting disc titles, artist names, or cool cover art. I usually walk out with 20-30 new (to me) CDs, for less than $10.

When you're done with the CDs you have, you can bring them in, and the store will buy them from you. You can take cash, or store credit (usually 150% or so of the cash offer). Take the store credit, run back into the trenches, and come back with another pile of unknown geniuses.

Buy, Listen, Sell. Repeat as desired

One advantage of second-hand music stores is that the staff sometimes actually know their music. Unlike the pimply teenagers at the mall outlet who think Puff Daddy invented rap music. So no worries about asking for Mojo Nixon, only to get "No man, he don't work here!" in reply...