What if you made the mushrooms giant, so that they became a surround for each players buttons? I think I agree with veinman that you'll be paying a lot for something that could be closely approximated with an inexpensive piece of countertop laminate. If you like the mario theme, maybe throw some blocks / coins / flowers in there? Even some of those green tubes that take you to a dungeon level, or a dungeon level itself might be cool. Again, very much a personal preference but thought I'd share mine!
wm