I never understood giving games to Gamestop, the price they give you isn't worth the value of owning the game. I recommend gamefly for people who don't like to keep video games. It's certainly cheaper than giving games you just bought to gamestop.
When insulting others, wielding proper grammar and punctuation is like holding up a shield that protects against contradiction.
Typical trade in value for a game just released is $25-35 depending on supply and demand. You can however get an extra 10% on top of that if you have an Edge or Power Up Rewards card. From personal experience the average trade in price seems to be 1/3 of their price for buying it used but that too can change depending on if they have copies in stock and if there's a demand for a paticular title. In fact believe it or not the price can actually be different from store to store. As a result it's hard to pin an actual trade in value onto a game.
As another option to buying games that you have a feeling to may trade in shortly after purchase you can also try My Coke Rewards for free Blockbuster rentals. 27 caps will give you enough points for one game rental. Hell even if you don't have a free rental I feel that $9 US for a five day rental is a much better investment in a game that is likely to collect dust after the first playthrough. While Fable is a decent series overall it's one that I feel never warrents the full price of a new game. Hell I didn't even buy Fable 2 until the game went platinum and was only $20 new. If I buy the third at all it'll be once the price drops.