If you can get to Target before October 1st (and before they run out of supply), the Logitech MX518 is on sale for $30 (it might still show for $40 or even $50, but price scan it and it should be $30 and check out as $30). This mouse has plenty of tried and true buttons, plus you can adjust DPI without drivers and thus avoid screwing with Apple's horrible mouse sensitivity settings.
I know how you feel though, I have to use a C2D iMac in one of my classes and I can't stand the mighty mouse. For me it isn't just the button(s) - the tracking just sucks in comparison to the mice I use, I bring in my own to use in class.