AnkerDirect via Amazon offers Prime members the Anker Wireless Vertical Ergonomic Mouse
, model no. AK-A7809012, for $13.59
with free shipping
. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $8.28.) That's the lowest total price we could find by $3. It features a sensitivity adjustment button (800, 1,200, or 1,600 DPI); next page and last page side-buttons; and is compatible with Windows, Mac, and Linux.