Earlier quoted context omitted.
How much manpower and energy does it take to make a paper US dollar with nothing backing it up? [EDIT] Since I'm getting downvoted, I'll answer my own question: $0.042 every 18 months.
I'm guessing that's the cost of printing a single dollar bill. There are also hundred-dollar bills, which presumably cost the same. It'd be pretty interesting to get the total cost of printing, transport, and storage, and compare to the cost of maintaining a similar amount in bitcoins (which I calculated here: http://news.ycombinator.com/item?id=2602667 ).
http://www.enchantedlearning.com/math/money/bills/one/
I didn't count the $100 because I don't believe they're printed/circulated/destroyed/reprinted as heavily as the $1. Who knows about the 5, 10, 20 and 50.
I also don't think this $0.042 covers the labor cost of distributing, collecting, securely shredding and tracking the movement of all these bills through the system every 18 months.