With your 40 dollars, buy the God of War collection and play it together. Once he has fun with that HE WILL WANT GOD OF WAR 3.
If he still wants MW2, then he's probably the shooter type of guy, then I'd just save up to buy GOW 3 and play it in his face. RUB IT IN. Show him the awesomess but don't let him play..... although that would be too cruel for anyone. LOL