Iran war cost hits $38 billion, forecast to rise $3 billion a month, CBO says ↧ ↧ Iran war cost hits $38 billion, forecast to rise $3 billion a month... The six-month-old U.S. war against Iran has cost $38 billion so far and ​that amount is projected to rise by $3 billion a month, Congress' nonpartisan bookkeeper reported on Tuesday, as the Trump administration ‌searches for ways to end the conflict and reopen the vital Strait of Hormuz.