Check your local Craigslist and Facebook Marketplace, no use selecting a pin or two to look for as you may never find those local. See what the market has local to you. Maybe start with a single player game as those are a lot simpler to diagnose and track down issues. Make sure you look it over before buying and that it works. Don't buy a project for your first machine. I can find nice single player EM machines fully working around me for $300-$600 and up depending on title.

Double this advice if you have a significant other who may not be happy about a machine taking up space for months as you work through it. I feel your first pinball purchase should be a solid machine that everyone in the family can enjoy. Then as things stop working as expected you can come back here, post questions, get help and work it out. It easier to say, "Everything worked but this one thing stopped working" and get help then saying nothing works and you are not sure it ever did. Plus you will have to start buying tools and specialty parts to test out solutions and it can get frustrating.

Of course if you have been working with electronics and such your whole life and you have a basement full of tools that is one thing but for most people a fun first machine will be the best way to get started in the hobby.