Řešilo se to tady mnohokrát....
https://pc.poradna.net/questions/2965577-windows-10-licence-za-100-200-kc-aukro-ebay-legal
https://pc.poradna.net/questions/1773780-win-10-licence-koupe
https://pc.poradna.net/questions/1768559-jak-na-levny-windows
https://pc.poradna.net/questions/2918549-windows-10-digitalni-licence
https://pc.poradna.net/questions/2799711-koupe-licence-klic-windows-10-jak-to-funguje
https://pc.poradna.net/questions/298333-windows-z-aukra
https://pc.poradna.net/questions/1555200-kde-koupit-windows
atd....
Máme tu i článek
https://pc.poradna.net/articles/2965607-zprava-o-upgradu-z-windows-7-na-windows-10-u-duchodcu