Logitech offers its “dented box” Logitech M570 Wireless Trackball Mouse, model no. 997-00013, for $39.99. With free shipping, that’s tied with our April mention (which involved padding hassles) and the lowest total price we could find now by $10. Sales tax is added where applicable. Features include programmable buttons, storable USB 2.0 receiver, 2.4GHz wireless, up to 18 months of battery life, and more.
Of note, this is a dented box item; while the packaging may be dented or scratched, the product itself is new with a full Logitech warranty.