The CBO has estimated the cost of the war based upon two scenarios:
Summary At the request of Chairman Spratt, the Congressional Budget Office (CBO) has totaled the funding provided through fiscal year 2007 for military and diplomatic operations in Iraq and Afghanistan and other activities associated with the war on terrorism, as well as for related costs incurred by the Department of Veterans Affairs (VA) for medical care, disability compensation, and survivors’ benefits. In addition to totaling the funding provided to date, CBO has projected the total cost over the next 10 years of funding operations in support of the war on terrorism under two scenarios specified by the Chairman. Those scenarios are meant to serve as an illustration of the budgetary impact of two different courses in the war on terrorism but are not intended to be a prediction of what will occur.
Appropriations for U.S. Operations in Iraq and Afghanistan and for the War on Terrorism (Billions of dollars)
Including both funding provided through 2007 and projected funding under the two illustrative scenarios, total spending for U.S. operations in Iraq and Afghanistan and other activities related to the war on terrorism would amount to between $1.2 trillion and $1.7 trillion for fiscal years 2001 through 2017 (see Table 1). A final section of this testimony briefly compares parts of CBO’s estimate to a frequently cited estimate prepared by two academic researchers, Linda Bilmes and Joseph Stiglitz. ...
According to this,
there is an additional $700 billion in interest expenses bringing the total
(under the $1.7 trillion dollar scenario) to $2.4 trillion. There is more to say but, unfortunately, I am short on time, so I will leave it to you to add more detail in comments. [Update: More here.]