The Iraq War Will Cost Us $3 Trillion, and Much More

excerpt:

Some people will scoff at that number, but we've done the math. Senior Bush administration aides certainly pooh-poohed worrisome estimates in the run-up to the war. Former White House economic adviser Lawrence Lindsey reckoned that the conflict would cost $100 billion to $200 billion; Defense Secretary Donald H. Rumsfeld later called his estimate "baloney." Administration officials insisted that the costs would be more like $50 billion to $60 billion. In April 2003, Andrew S. Natsios, the thoughtful head of the U.S. Agency for International Development, said on "Nightline" that reconstructing Iraq would cost the American taxpayer just $1.7 billion. Ted Koppel, in disbelief, pressed Natsios on the question, but Natsios stuck to his guns. Others in the administration, such as Deputy Defense Secretary Paul D. Wolfowitz, hoped that U.S. partners would chip in, as they had in the 1991 Persian Gulf War, or that Iraq's oil would pay for the damages.
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The end result of all this wishful thinking? As we approach the fifth anniversary of the invasion, Iraq is not only the second longest war in U.S. history (after Vietnam), it is also the second most costly -- surpassed only by World War II

http://www.washingtonpost.com/wp-dyn/content/article/2008/03/07/AR2008030702846.html

I seem to remember not long after the war began they said it was costing us about 1 billion a day at that time.