Super Orbit is an ok game, alot of people knock it however. $500 seems a little high though. It books at $450 in my latest price guide. I really like the EM versions Outer Space/Orbit. The game just feels "right" in the EM versions as opposed to the solid state. Gottlieb was way behind the times on Super Orbit, I guess because of the price cutting at that time.
If the game is in decent condition I think $400 would be reasonable.