Don't be too hasty to unload it to what you think the first "reasonable" offer might be.
You may have something special on your hands: the 2010 Mr. Pinball price guide shows only 55 being made and has assigned a value of $$$ to the game.
I'm not sure exactly what $$$ means in actual dollars on this game; only that they usually only assign this symbol to games that command big bucks.
You need some expert advice now on this one.