Afghan War Cost: What can we afford?

I read today that the US counterinsurgency field manual recommends a soldier for every 50 residents of an insurgent region:
http://www.tnr.com/article/world/stalemate


Afghan population estimates range from 23-33 million people currently, with most estimates being near 30 million, (from an English language Google search of UN and CIA sources). Let's assume the population is 30 million. So an occupying force of 600,000 would be needed.

With non-US NATO troops at 34,000, the Afghan army currently near 100,000 and the Afghan police at 80,000, there would need to be about 386,000 more troops put up by the US.

How will McCrystal get it done with 40,000 over the 68,000 US troops already there? Won't he be 386k - 108k = 278,000 US troops short?

Then the expected cost of occupying Afghanistan successfully for the US would be 386,000 troops times US$1 million per troop, or about US$ 386 billion per year.
http://www.bloomberg.com/apps/news?pid=20601087&sid=aGvM0165Q9bs

If we can get local control set up in a decade (unlikely, says Rory Stewart, Harvard:)
http://www.hks.harvard.edu/news-events/news/testimonies/rory-stewart-on-afghanistan
then the total US cost would be US$ 3.86 trillion; if it took twenty years, the US cost would be US$ 7.72 trillion.

We have a US population of about 0.3 billion, so that is $26,000 per person, right? Can we get that kind of money? If we could, aren't there better things to do with the money? What will assuming this kind of debt do to the dollar's strength?