Ask HN: How do you manage licenses for Windows VM's?

I am doing some projects that require Windows OS, more specifically 1 embedded project that requires Windows for development and a couple of projects that are cross platform. I need clean environments that are separate from each other, they can't cross over so sharing one machine is not an option.

I work off a Macbook Pro and have parallels which works well, but I am trying to figure out if I have to buy three/four licenses of Windows 8/10 or if there is a better way to do it. I also would ideally like 1 or 2 clean test environments for Windows that I could blow away regularly and redo for testing. I used to use Volume licenses for this when we had them but I don't do enough Windows work to justify the cost of an MSDN Ultimate type subscription anymore.

Any suggestions?