All of my other hobbies are cheaper than pinball. I like to fish, fly fish, and kayak. Buying a few kayaks was the most expensive part. I'm cheap, so I don't buy expensive fishing rods. I enjoy making my own fly fishing flies and that's pretty cheap too.
My previous money pit hobby was trying to keep my 1992 Volvo 240 station wagon running. It was my transportation for 15 years and stuff was always breaking on it. I also enjoyed maintaining it, so it became a hobby. No car payment for the thing, but I dumped plenty of money into it to keep it running and as reliable as I could. I sold it for a used 2008 Honda Fit and have enjoyed trouble free driving ever sense. haha
I really would like to get one or two modern pins. My Flight 2000 keeps having problems. It now has flaky sound. I need to take a look at the sound board to see if it is anything easy to repair/solder. Ugh. Hopefully I don't make it worse.