This technology is still in development and so I have no idea what the cost is going to be. However, without considering costs, this may have potential for use in low resource settings:

“Morning Edition, August 27, 2007 · Blood and sweat could power a battery that looks just like a piece of paper, scientists say…the new paper battery can run on blood or sweat. That means it might ultimately be used to power medical devices like hearing aids or pacemakers.” NPR full story.