Overstock.com is offering a Refurbished Logitech Performance Mouse MX for $
44.99 + 10% off coupon (in sidebar, automatically applied), bringing the
final price to $40.04 with free shipping.
Link: http://www.overstock.com/Electronics/Logitech-Wireless-Performa
If you prefer new, head to logitech.com and use the 791191repp code for $64.
99 (new) + FS.