B&H Photo-Video offers the Microsoft Arc Touch Bluetooth Wireless Mouse, model no. 7MP-00001, for $49.99 with free shipping. That's the lowest total price we could find by $2. (Most stores charge over $60.) It features a flexible design, touch scrolling, BlueTrack technology, and purportedly up to six months of battery life.
Update: As a reader found, Amazon offers it for the same price.