Any computer store or big-box will have lots of good mousies for good pricies.
I'm still using the mouse I picked up back when Circuit City was still in business. Five buttons, built in charging cradle, all for #25. Unfortunately they don't seem to be made anymore, but there are lots of good deals here, of course:
http://www.amazon.com/Mice-Keyboards...pf_rd_i=172456