Shanti has dug out this link which talks of US Aid to Afghanistan. Total US aid given: $840 million.
This puts things in perspective:
American officials like to point to their spending in Afghanistan: $840m since October 2001, with plans to spend at a similar rate this year. That might sound like a lot, but it is little more than Iran, an impoverished country, has promised to its neighbour. In one astonishing oversight, the Bush administration failed to request funds for humanitarian aid and reconstruction in Afghanistan in the latest budget, prompting Congress to step in and allocate $300m on February 13th.(Economist)

Given that the Americans are almost completely responsible for letting Afghanistan slide into the Taliban rule, I’d have expected them to spend a little more on the “nation-building” they say they aren’t interested in.