Add up:
New York Times: “High Costs Weigh on Troop Debate for Afghan War”
The estimated $1 million a year it costs per soldier is higher than the $390,000 congressional researchers estimated in 2006.
A good short general treatment of the costs of “exporting democracy” is found in Chris Coyne’s After War: The Political Economy of Exporting Democracy. People who advocate a “Stay the Course” approach (or even expanding “nation building” exercises) should grapple with Coyne’s arguments and evidence.