At the bottom of the page abacab linked to, there was an ad offering
W10 Pro for $35 from an outfit called Allkey4U.com. I was suspicious, so I checked it out.
Unfortunately, there's a good chance it's a scam.
There are sketchy user reviews that say vague things like "they had what I needed and the price was right", and "Perfect! Exactly what I needed". Apparently, they are selling Technet licenses. Those are Windows licenses you get with your TechNet subscription, and are not supposed to be resold.