“If you want to find out how much the Pentagon’s military operations cost, Todd Harrison is your go-to guy,” The Hill reports.  

“Harrison, a senior fellow at the Center for Strategic and Budgetary Assessments (CSBA), tracks defense spending, and he estimated the possible costs of the fight against the Islamic State in Iraq and Syria (ISIS) before the Pentagon released comprehensive spending figures.”  

“A September report Harrison produced estimated that the war could cost the U.S. between $2.4 billion and $22 billion per year depending on the number of ground troops and intensity of air operations.”