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During the steam sale I've been hanging out for Castle Crashers to drop in price. It did by 50% but that was still $7-ish per game.
Just checked Amazon and they are selling it at $3.75.
It's a Digital Download from Amazon and as such does require an American Billing address. It does not need to match your card.
http://www.amazon.com/b?ie=UTF8&node=6923534011
"75% off July 18-24."