I, too, have a cordless keyboard and mouse. With so many other wires going to and from my computer (printer, modem, monitor, etc.), I prefer as much cordless as I can get.
I seem to go through the batteries more for the mouse than keyboard. I just haven't kept track numbers-wise. Or brand-wise.
Here's the good news for me...a month or so ago, I was looking for a new mouse because I had been using a "loaner" with a cord (long story).
Lo and behold, I found a cordless Logitech mouse at Target (I believe it was $29.95) that has an "on/off" switch. So when I turn my computer off at night, I turn off the mouse, too! And save my batteries lives!