Amazon offers Prime members the Logitech Trackman Marble Mouse, model no. 910-000806, for $17.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $8.54.) Although we saw it for $2 less in January, that's the lowest price we could find now by $3. Features include ambidextrous trackball design, USB, and fingertip-based control.