I don't mean to quibble, but Iraq isn't exactly a war anymore. The old Iraqi governemnt of Saddam Hussein is destroyed, and the main combat is finished. Violence still drags on.
How much is this "isn't exactly a war" costing us a day?
Lessee, the budget amount is $144,000,000,000 (my inner child says, "That's skazillions.") for fiscal 2009. Compare this to planned budgeted social spending increases for fiscal 2009 of $682,000,000,000. Social engineering is a legitimate comparison, since we are in that biz in Iraq as much as here. Whether it is legitimate to engineer American society is another question.
Compare the situation to the conclusion of World War 2; the parallels are extensive. At the of main combat in Europe, Germany was crawling with "Wolverine" units. Wolverines were Nazi revenge thugs who murdered German people and occupying troops. Support came from abroad, financed mainly through (not by) neutral Switzerland, directed from Argentina, and to a lesser extent Brazil.
The US still maintains forces in Germany. If the WW2 victory is portent, the hostile phase of the occupation in Iraq will continue for another decade. US will maintain forces in Iraq for at least the next half century.
I must admit Germany was surrounded by our Allies (for example, Russia :-) making such an occupation much more tenable.
At the conclusion of WW2, Europe was prostrate. The rebuilding was financed largely through the US.