Learn to fix ( which most people can do if they are interested enough)

Or buy a working one

To fix you will need a good soldering gun, magnifying glass, and contact crimpers. About $200 for all. Hours of reading ( which is not really that complicated)

The MPU on many Bally games from that era are FUBAR, the power supplies are shot, the rectifier boards need rebuild, the connectors need repinned, the pins on every board at minimum need resoldered if not replaced. There's other issues to learn. Those are just the most common. The game is almost 40 years old. It has to be rehabbed to make it reliable. Once you learn how to do all that stuff you can fix one up pretty quick. There is a price for entry on the first one.