Logitech has the Logitech M570 Trackball Laser Wireless Mouse (new, dented box) for $40 with free shipping. Features hand-conforming sculpted shape, thumb controlled trackball, three customizable buttons and scroll wheel.
I have the wired version of this and wouldn't go back to any other type of mouse. Since you don't move the mouse, I wouldn't think that it would be that big of a deal to have the wire attached. There are trade offs with a wireless mouse: either re-charging or replacing batteries and I had one that had a "battery saver" feature that meant I had to give it a wake up shake. I'll stick with my wired trackball.
I have the wired version of this and wouldn't go back to any other type of mouse. Since you don't move the mouse, I wouldn't think that it would be that big of a deal to have the wire attached. There are trade offs with a wireless mouse: either re-charging or replacing batteries and I had one that had a "battery saver" feature that meant I had to give it a wake up shake. I'll stick with my wired trackball.