Newegg offers the refurbished Logitech G100s Optical Gaming Mouse, model no. 910-003533, for $18.99. Coupon code "EMCPCWB43" cuts it to $14.24. With free shipping, that's $3 below our April mention of a new mouse and the lowest total price we could find for a refurb by $2. It features an ambidextrous design, 250 dpi to 2500 dpi tracking resolution, and speed of up to three meters per second.
A 90-day warranty applies, but it's unclear who backs it.