Why do most people even need a PBX?
For the call centre yes, but for the majority of desk based places I've worked I've never needed to touch the phone on my desk. All my calls can be handled with Teams or Hangouts or flavour-of-the-month, and on the odd occasion that I need to actually phone someone I use my moby.
So, that's one way people could save money. Just have a phone shared by a bunch of peeps, which you can use for emergencies. One per block of desks, or perhaps one per floor. Give it a wipe down regularly of course.