Amazon offers Prime members the Logitech G402 FPS Gaming Mouse, model no. 910-004069, for $34.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $8.48.) That's the lowest total price we could find by $11, outside the prices below. (For further comparison, last month we saw it for $4 less.) It features four on-the-fly DPI settings (250 to 4,000 DPI) and eight programmable buttons.

A couple close prices: ClaimThis via eBay and 3B Tech offer it for $38.99 with free shipping.