Score Mighty via Amazon offers Prime members the Dell WM324 Wireless Optical Mouse
with free shipping
. (Non-members can spend $35 to qualify for free shipping; otherwise, it adds $8.) Outside of the mention below, that's the lowest total price we could find by $18, although we saw it for a buck less during Black Friday weekend. It features Logitech unifying technology (manages up to six peripherals) and an ambidextrous design.
A close price: Dell Home
offers it for $14.39 with free shipping via coupon code "1FJX7RT130KJL2".