Anthony Cordesman tries (pdf):
The fact remains, however, that if the CRS and OMB figures for FY2001-FY2013 that follow are totaled for all direct spending on the war, they reach $641.7 billion, of which $198.2 billion – or over 30% – will be spent in FY2012 and FY2013. This is an incredible amount of money to have spent with so few controls, so few plans, so little auditing, and almost no credible measures of effectiveness
As Cordesman also notes, it's laid the foundation for a tremendous amount of Afghan corruption and created a state so precarious it could easily collapse as the funding is withdrawn - as it must be, over time.
It will be interesting to see if the self-styled stewards of America's fiscal responsibility will have anything to say about this. Just today, National Review published a piece lambasting the (admittedly poor) investment in GM which soaked tax payers to the tune of about $66 billion. I wonder what they'd make of the hundreds of billions invested in Afghanistan - a growing share of which is being spent on President Obama's watch.