how the hell can you get 40-50 bucks for this game? Do you mean selling it online/to a friend?
Anyway, here is my advice: no matter what game we are talking about, DLC only really adds a little to the overall product. Dragon Age, Alan Wake, Dead Space 2... though they all ended up with DLC, the content added was only a few hours worth in the end, which is probably not worth the 40-50 you would make. So ask yourself this question: will you want to play this game again? If the answer is yes (even a slight yes) hold onto the game, because as soon as you get rid of it, you will want to play it again, and no one likes rebuying games. If you can honestly say that you will NEVER want to replay the single player campaign or coop or online anything, then go ahead and sell to pick up a new title. But trust me, if you get rid of a game you're not done with, you will seriously regret it.