I'm still awaiting word on a lower-cost source for the batteries.
http://www.batteryjunction.com/en392384siox.htmlEnergizer silvers, they start at 90 cents, and drop to 60 if you buy more than 10 of them. However...
http://www.batteryjunction.com/onemalrmialb.htmlMaxells start at 99 cents but drop to 50 if you order ten or more. So for ten bucks, plus a little shipping, you can get five full sets of spares.
Any cheaper, and you have to whack little old ladies over the head and steal their hearing aids.