Buy.com via Rakuten offers the IOGEAR Multimedia Wireless Keyboard, model no. GKM561R, for $34.99 with free shipping. (Amazon charges the same.) That's the lowest total price we could find by $3, although we saw it for $7 less in July. This 2.4GHz keyboard features a laser trackball, scroll wheel, 19 multimedia hotkeys, on/off switch for battery conservation, and more. It requires two AA batteries (included).

Note that while this keyboard is Mac compatible, the multimedia hot keys are not supported.