B&H Photo Video offers the Kensington Orbit Trackball with Scroll Ring in Black, model no. K72337US, for $19.95 with free shipping. (Newegg and Amazon have it for about the same, the latter exclusively for Prime members.) That's the lowest total price we could find by $4. This USB trackball features an ambidextrous symmetrical design, two buttons, optical tracking technology, and scroll ring.