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 $35 or more to qualify for free shipping; otherwise, shipping costs $8.39.) That's $5 below our July mention and the best total price we've seen for a new one. (It's a current low by $7.) Features include programmable buttons, 2.4GHz wireless, and up to 18 months of battery life. Deal ends today.