Newegg offers the refurbished Logitech G402 FPS Gaming Mouse, model no. 910-004069, for $24.95 with free shipping. That's $14 under the lowest total price we could find for a new unit. It features four on-the-fly DPI settings (up to 4,000 DPI) and eight programmable buttons.

A 90-day warranty applies, although it's unclear who supports it.