There's an Official Easter Egg in the DOS version of Monopoly Deluxe. When the game has just started, the white letters JMA are barely visible in the upper right-hand corner. JMA stands for Juan M. Alvarado, the programmer of this game. To activate the Easter egg, click on the letters JMA. (This step is not shown in this video.) In v1.5 you'll first have to close the window that pops up when you start the game.
Then when a new game has started, set the Free Parking Ante to $865.

Official Easter Egg

What? The project is over? I can
come out now?

Click Ok to release the
programmer.

I'm Free!

Thank you for releasing me. I will
now grant you three wishes. Just
kidding. I think I'll hang out in the
parking lot if you don't mind.