I love my cordless optical Logitech MX700 mouse. It cost about $60 (but had a rebate), but no batteries! It has a recharger base. I use it all day, almost non-stop, then at night when I turn off the computer I put the mouse in its recharger. Works great!

My mom has a cordless optical that uses batteries and it eats them. She has to change them at least once a month, so the extra cost of my mouse has paid for itself by not having to buy batteries. Plus, no frustration of having the mouse die in the middle of something you're trying to get done.