What is the cheapest legitimate way to activate Windows 11?

[sb644098]

I'm setting up a PC and trying to figure out the most affordable legitimate way to activate Windows 11.

I know Microsoft sells Windows directly, but I've also seen much cheaper keys being offered through Amazon and various software-key retailers. The price difference can be pretty significant, so I'm wondering what actually explains it.

A few things I'm trying to understand:

Is upgrading from an eligible Windows 10 installation still an option?
What's the difference between OEM, Retail, and other Windows licenses?
Are cheaper product keys from third-party sellers legitimate?
Is there any real difference after activation?
What should I check before buying a key online?

I've seen people mention Microsoft, Amazon, DigitalLogs, and NoxKeys, but I'd rather hear from people who have actually purchased and activated Windows 11 themselves...

What's been your experience, and which option did you end up using?