My advise is this.... pace yourself. Post a few "wanted pinball machine(s)" in your local craigslist and see what your response is. And religiously search CL as well (but you are up against a half a dozen other collectors doing the same thing) so get the craigslist app on your iPad / iPhone that notifies you when your search results are met (obviously searching for "pinball" and don't forget "pin ball") check it several times a day. Yes you have to work hard to find a good deal, but the hunt is part of the fun. AND expect to drop everything and immediately go get a machine when you see something you like... otherwise someone will beat you to it.
On any high dollar item... if you MUST have it today you will be paying full price for it; like if your refrigerator goes out, you have no choice.... you have to go find one that day and buy it. That puts you in a weak purchasing position.
My advise is get one game at first that you really like, it is okay to pay a bit more for it. Then add to your collection as you go, remember you can resell pins you get tired of.
Avoid project machines that will require a lot of work you are not willing to do.