I have no idea what my used 06 Langster frame is worth. I am getting a new frame soon and am going to put the Langster frame on craigslist. Cosmetically its in decent shape (normal wear and tear, no major scratches or dents though). I will be including the stock seat post and headset if the buyer wants them.
I think that is about right. If I were looking for one that is what I might pay. You can check ebay completed listings and see if any frames sold on there and what price. I would stick with CL. I don't think there will be a huge demand on ebay for the frame. The buyer will have to pay shipping and you will have to spend your time packing it and buy the materials to do so. Not to mention the ebay and paypal fees.
I think Philadelphia would be a big enough fixed gear market to sell it on CL. If you were in the middle of a corn field small town then you would have to go with ebay. You will just have to wait until the right buyer sees it on CL. Take really good pictures and put them in there big, not with the small CL picture insert feature. And make sure it's as clean as you can make it.
I live in a huge market, (SoCal) and seldom see Langster frames so IMO it should sell easily if you price it fairly.