How much can I get for my LG Doubleplay if I sell it? And how can I sell it?

I've upgraded from my LG doubleplay to and Iphone 5 and It would be nice if i could make some quick cash from my double play. How could I sell it? Would T-mobile buy it for me or is there a website I could sell it on? Answers quick please1

I sold my 2 years ago n got 100$ so your gonna get 50$ I'd go with gazalee