$230m for just blowing stuff up, no advanced special effects? That’s way too high, I’d be surprised if it was more than $100 or so.
I don't know where this $230 mil figure appeared. Not even Avatar cost that much. The best I can find for the reported budget of The Green Zone was, as you said, around $100 mil. Still a lot of cash for a $14.5 opening weekend (which is, sadly, $2 million better than The Hurt Locker's entire theatrical run).