As pricing deals go, the Microsoft wireless Explorer mouse is $39.95 at Sam's Club.
It is similar to the Explorer in colour and number of buttons, but it has a few subtle differences. The rolling wheel is a little straighter in angle to the body of the mouse (as compared to the one on the normal Explorer). The overall mouse is taller in order to accommdate an inset area for your thumb. Because of the inset area for the thumb, the wireless Explorer is more comfortable (for me) to hold or rest my hand upon. If you have sticky (or moist/grimy) hands, the regular explorer is fine because you don't have to spend any energy gripping the mouse with your fingers. If you have clean dry (non sticky) hands, the wireless Explorer mouse may give you an improved ergonometric feel.