Where to buy an actual legit Windows 8.1 Home product key that isn't extremely expensive

[paradise14z]

-This is my first post-

So earlier today my boot setup crashed on me and I had to boot to a recoverable disc.

I installed a new CPU (AMD FX 8350) and my computer immediately shut off.
Restarting it I was greeted with a message about my boot setup being corrupt. My PC is custom built by CyberPowerPC about 2 years ago and they gave me a Windows 8.1 disc included (The OS it originally had).
However the CD that was included was just a boot disc and not a registered copy.
The PC has no stickers on it about a registry key. Theres NO product key that came with this computer.

MY PLAN: Buy a Windows 8.1 product key, register this current version I'm on and simply upgrade to Windows 10 for free afterwards.

I'm looking for a Windows 8.1 Home Edition Product Key to buy online that isn't about 120 bucks.
I looked around a bit and anything cheaper than 120 is from a unknown source and I'm immediately worried about purchasing their codes.

I'd love to know where to look to buy a product key.
Or if I'm going into this process and someone knows this won't work I'd love the help. I'm at the end of my rope today.
-Thanks everyone

 

[ShaolinDee]

You can no longer upgrade to windows 10 for free but if you have built your own PC, you can download a Windows 10 ISO from Microsoft's website: https://www.microsoft.com/en-gb/software-download/windows10 and then purchase an OEM key from https://www.kinguin.net/category/19429/windows-10-professional-oem-key/ (This site also offers insurance for your key) This will only work as a fresh install though, so you would need to back up any files, programs etc to an external device and then reinstall them once you have upgraded to Windows 10.

 

[panda32]

Yeah with OEM keys you have to do a fresh install, I brought mine from here, https://www.softwarepros.co.uk/product/windows-8-1-pro-key/ They also provide installation instructions with the key.