I've found a MX-900 from an authorized URC dealer willing to give me the software that's in my price range. Though it's closer to the MX-500 in display, it does have 7 characters for each label instead of five, and its PC programmable. I also understand it has variables available for storing the state of button pushes, etc.

I'm seriously thinking about going with the MX-900. Other than the icons, color, and longer names on the LCD screen, any differences between the MX-880 and MX-900 I should be concerned about?