They've always been hard to get. When you first start out ANY pinball machine will do and that is pretty straight forward to find. Once you are deep into the hobby it becomes a chase on titles and that has always been difficult.
Ive been collecting projects in Australia for 20 years now and even 2 decades ago I would come across a standard 70's Williams EM sitting on a back deck rotting under the weather and the owner was convinced they would be able to retire on its sale. A $100 basket case is still a $100 basket case!
A fully working and tidy Bally Lost World ( great machine) I sold for $1400 8 years or so back. Id still say that title is worth that amount despite seeing them on Ebay with an asking price nudging $3000. If I had one to sell today, my asking price would not have changed.
Most ive ever paid was $3000 for a woodrail I ended up selling for $1200. The right price there is the $1200.. I got ripped at $3000 but I learnt the lesson!