Joseph Stiglitz, a Nobel prize-winner in economics, says the Iraq war has cost $3 trillion so far. According to the Guardian, "three trillion could have fixed America's social security problem for half a century."
Some time in 2005, Stiglitz and Linda Bilmes, who also served as an economic adviser under Clinton, noted that the official Congressional Budget Office estimate for the cost of the war so far was of the order of $500bn. The figure was so low, they didn't believe it, and decided to investigate. The paper they wrote together, and published in January 2006, revised the figure sharply upwards, to between $1 and $2 trillion. Even that, Stiglitz says now, was deliberately conservative: "We didn't want to sound outlandish."
So what did the Republicans say? "They had two reactions," Stiglitz says wearily. "One was Bush saying, 'We don't go to war on the calculations of green eye-shaded accountants or economists.' And our response was, 'No, you don't decide to fight a response to Pearl Harbour on the basis of that, but when there's a war of choice, you at least use it to make sure your timing is right, that you've done the preparation. And you really ought to do the calculations to see if there are alternative ways that are more effective at getting your objectives. The second criticism - which we admit - was that we only look at the costs, not the benefits. Now, we couldn't see any benefits. From our point of view we weren't sure what those were."
Link (Thanks, Robert!)