As one of its daily deals, Amazon offers Prime members the Logitech M570 Wireless Trackball, model no. 910-001799, for $27.50 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $8.51.) That's $2 under our August mention and the lowest total price we've seen for a new one. (It's also a current low by $8. For further comparison, we saw a refurb for $25 shipped three weeks ago.) Features include programmable buttons, 2.4GHz wireless, and up to 18 months of battery life. Deal ends today.