I highly recommend buying an old pinball machine and refurbishing it yourself. You'll learn a ton about how these great machines work. I got an old Creature From the Black Lagoon (1993) [1] and stripped down and rebuilt all of the playfield and the cabinet. There's lots of info on the web about how to fix them, and many companies sell spare parts.
[1]http://www.ipdb.org/machine.cgi?id=588