As one of its daily deals, Amazon offers Prime members the Logitech M570 Wireless Trackball, model no. 910-001799, for $20.25 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $8.58.) That's $7 below our mention from two weeks ago and the lowest total price we could find now, also by $7. Features include programmable buttons, 2.4GHz wireless, and up to 18 months of battery life. Deal ends today.