Walmart offers the Logitech M570 Wireless Trackball in Gray/Blue for $24.99. (Best Buy and B&H Photo Video offer it for the same price.) Opt for in-store pickup to dodge the $5.99 shipping charge. That's tied with our mention from a month ago and the lowest price we could find by $15. Features include programmable buttons, 2.4GHz wireless with a 30-foot range, and up to 18 months of battery life.