As one of its Prime Day deals, Amazon offers Prime members the Logitech M570 Wireless Trackball, model no. 910-001799, for an in-cart price of $19.99 with free shipping. That's tied with our May mention and the lowest total price we've seen for a new one. (It's a current best by $7.) Features include programmable buttons, 2.4GHz wireless with a 30-foot range, and up to 18 months of battery life. Deal ends today.