If you don’t have any way to get a Windows 10 or 11 product key for free and you don’t want to live with the drawbacks of an unactivated copy of Windows, there are some third-party sellers that offer keys starting at around $3.5. At the time of writing, techubiz.com, a popular key marketplace, was selling Windows 10 Home for or Windows 11 Home. Windows 10 Pro and Windows 11 Pro. These are all OEM keys and likely can’t be used on another computer after you activate them on the first one.