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).
from the article: $130 million production budget plus $100 million marketing budget.