The least expensive one is a Broderbund product powered by Virtual Mechanics. I doubt the product is identical to the one sold directly by Virtual Mechanics, it may be based on an older version with fewer features.

I also had Windows 7 and followed the prompts to upgrade to Windows 10, once upgraded and activated I performed a clean install of Windows 10 on a different drive skipping any prompts to enter my Windows 10 key (which I don't know). My copy of Windows automatically activated after I connected to the internet wirelessly and without entering a key or providing my email or any personal information.  As michaelkenward stated looks like once your machine is activated Microsoft stores your PC's "fingerprint" on their activation servers and will automatically activate Windows on the same machine.  That same day I tried a clean install of Windows 10 in a different language and it also activated automatically after I connected to the internet.

I will take one, please. I have an older version.