Meritline offers the open-box Microsoft Notebook Optical Mouse 2-Pack in Silver, model no. M20-00001, for $12.99 with free shipping. (Choose the second option under "Buy More Save More".) That's the lowest total price we could find for this mouse in this quantity by $11. Features include an optical sensor, clear scroll wheel, and more. A 1-year Microsoft warranty applies.

Of note, Meritline also offers a single Microsoft Notebook Optical Mouse for $9.99 with free shipping.