Or you can always take a jaunt to Baltimore and go to either one of the Record & Tape Traders, CD Depot, or better yet, Soundgarden in Fells Point. If you have or are looking for a lot of Hardcore, try Reptilian Records in Fells Point. Don't know if they have a used section but I have a feeling they do. Hardcore isn't my thing but I know that's the place to go for that type of music. Could make a day of it between Reptilian and Soundgarden, both within easy walking distance. Top the night off with seeing a show at Flecther's.
I've never sold any CDs so I don't know who gives the better prices. Soundgarden tends to have the better prices for buying and more selections but it really all depends on what you're looking for and when you hit either store. Both are pretty good. Sonick can give you the lowdown about selling at R&TTs.