No more than "50-75 'al-Qaeda types' in Afghanistan", according to the CIA, have been responsible for draining the US government by no less than US $10 billion a month, or $120 billion a year.
At the same time, outgoing US Defense Secretary Robert Gates has been adamant that withdrawing troops from Afghanistan is "premature". The Pentagon wants the White House to "hold off on ending the Afghanistan troop surge until the fall of 2012."
That of course shadows the fact that even if there were a full draw down, the final result would be the same number of US troops before the Obama administration-ordered AfPak surge.
And even if there is some sort of draw down, it will mostly impact troops in supporting roles - which can be easily replaced by "private contractors" (euphemism for mercenaries). There are already over 100,000 "private contractors" in Afghanistan.