Kodak 5200 mAh Powerbank: $15 at Safeway/Woolworths 150 grams (139 minus cord). This is cheap enough you could just use it once (instead of 500X!) then throw it away! Doesn’t the world just keep getting better and better?
Of course there are lighter (if not cheaper) options. For example, I usually carry a spare battery for my mobile phone (about 30 grams). I also have a Bruntons Solarwrap Mini Solar Charger which weighs 85 grams and contains a 2200mAh battery.
See also:
http://www.theultralighthiker.com/charging/
http://www.bushnell.com/hunting/outdoor-technology/powersync/solarwrap-mini
http://www.theultralighthiker.com/power-from-heat/
http://www.theultralighthiker.com/mobile-phone-battery-life/
http://www.theultralighthiker.com/clear-pvc-backpack-lid-for-solar-charger/
http://www.theultralighthiker.com/supercharging-led-torches/
http://www.theultralighthiker.com/eneloops-rechargeable-batteries/
http://www.theultralighthiker.com/eneloop-pro-aaa-battery/
