As you may know, Apple does allow unlimited use of MacOS in VMs, as long as the VMs are running on Apple hardware.
So, for example, my MacMini Has VMware Fusion, and I can create VMs running MacOS at will (very useful for testing potentially destructive programs or developing system code).
So if you're willing to spring for one Mac Mini plus $80 for Fusion, you have what you need to run multiple instances of MacOS (in VMs).
I know, that's not quite what you are looking for. Just trying to be helpful... :-)
Interesting thought. Does the Mini typically come with media? I'm pretty sure I can use a Fusion VM in vmware.