Looks like the Iraqi war came in very close to its budget:
A short conflict that used fewer missiles, sparked fewer oil field fires and created fewer refugees than anticipated produced a lower-than-expected financial cost for the major combat in Iraq…
…A detailed account of expenses won’t be complete for months, but senior administration officials say the cost of deployment and combat will be just less than the $62.6 billion Congress approved in March as emergency funding for Operation Iraqi Freedom. It is the first time officials have offered a tally. [USA Today, “Short conflict, less ammo kept war cost down”, June 13, 2003]
Some other interesting points from the article:
The price for the combat phase is about $220 per American. The Persian Gulf War in 1991 cost $76 billion in today’s dollars…
Planners budgeted $593 million to care for as many as 2 million refugees, a problem avoided when urban combat was less extensive than expected. The refugee count was less than 100,000…
…$200 million was earmarked for emergency food supplies for Iraqis, but no major shortages occurred. [USA Today]