I'm not sure what the GameStop's are like in your area, but where I live most used games that are on their racks a few days to a week after a new game comes out are at most $5 off. I've seen as little as $2. Considering that Best Buy purchases titles in huge bulk, they can probably afford this, since their bulk pricing gives them more profit margin to play in.
The other thing you are forgetting is that Best Buy is also hoping when you come in to buy that new video game at a used game price, you might also pick up a CD or DVD, maybe an accessory, heck even some candy or a soda, then they make more money. You came in ready to spend $50 - $60 (with tax included) and you droped $75 - $100. They are willing to lose a little money on one side and hope they profit on the other.
The other thing you are forgetting is that Best Buy is also hoping when you come in to buy that new video game at a used game price, you might also pick up a CD or DVD, maybe an accessory, heck even some candy or a soda, then they make more money. You came in ready to spend $50 - $60 (with tax included) and you droped $75 - $100. They are willing to lose a little money on one side and hope they profit on the other.