If you're handy with a soldering iron:
I bought a 5/6V 3amp BEC from eBay - it's intended to be used to power the receiver and servos of a model aircraft.
LINK
It will convert anywhere between 5.5-23V down to 5 or 6V (user selectable).
They are $4.50 shipped.
I'm using one for the RA drive on my EQ3. They could also be useful for powering USB hubs in the field - they usually require 5V.
DT