Found this today. Thought it was useful information.

QuoteYou can spend thousands on components for building a PC, but it won't boot without an operating system (OS). Linux is a viable option, but most prefer Windows because it runs all their favorite software, including the latest games. Windows 11 isn't here yet, but fortunately, you can get Windows 10 for free or cheap -- if you know where to look.

https://www.tomshardware.com/reviews/get-windows-10-free-or-cheap,5717.html

For me it's just a matter of buying an OEM key every time I build a new PC, normally about £20. Always worked and never had MS deactivate any of the keys.

Good info though 

Have you got a link to a website that offers the cheap keys please, just in case?

The below site has been selling OEM keys for many years and hasn't been shut down:

https://www.kinguin.net/

Datahopa.co.uk is not affiliated with the above site.

Excellent, thanks