Don't know about GameStop but right now EB gives $50 for an XBOX. During the winter sale between 1/13 and 1/22 they'll be giving an extra $10, so that would be $60 assuming they don't change the base price.
Trade values should be the same now, they've been spending the past few weeks/months trying to synchronize most of the trade values to make the POS and inventory merging easier come Feb.
