Funny how we were not terribly concerned about deficits until a Democrat became President. Anyway, the costs of an additional soldier sent by the US to Afghanistan amounts to $1 million per. Any "surge" is going to add billions a year, so that the savings from departing Iraq will be wiped out by the increased costs of operating in Afghanistan. So, Obama may need Republicans to vote for his defense programs to cover the gap caused by Democrats voting against more $$ being spent on foreign missions.
So, the mission going forward is incredibly costly (see here for previous post on this topic). Still, this math ignores the cumulative cost over the next fifty to seventy years--the health care costs and disability payments to the soldiers who survive their wounds.