D cell batts are the most economical portable power next to the 6V lantern battery (which is 1/2 the cost per watt hour)... get some D batt holders and power anything you want cheeeeply.. what happened to the mag that you aren't using them there?
Find somebody with a D mag and make a trade of some kind...
make a 1cell D-powered micro lux similar to my micromighty... but obviously with a driver.. it's a very small light and since only running 400mW it'd run forever..