I recently tried to trade in my Gears of War 2 (SE) and Assassin's Creed at my local EB Games/Gamestop and was only offered $12 and $4 respectively and I declined.My ballpark estimate says you shouldn't be offered too much more or less. Also, i don't know if they will take your Perfect Dark Zero because of its age and value. All in all, you may not have enough considering that CoD: WaW is still valued at $60. If you feel like your being swindled than just don't do it because I'm pretty sure Gears of War 2 is worth way more than $10-$20 and its still a best seller, glad I held on to mines. Good Luck
XBL Gamertag: Fenderstrat 14