I get a Windows 10-based newsletter from Windows Chimp. It's usually just information and today a warning about some new malware. But a couple of times they have offered a license for Windows 10 Pro for $79. It is $190 - $200 at Newegg and Amazon. This is a full retail version which you can use to either upgrade or do a full clean installation.
I have purchased two of these licenses from Windows Chimp and both worked perfectly. You would need to download the Media Creation Tool from Microsoft and then when prompted during your installation, enter the license.Media Creation ToolWindows Chimp
I have no idea how long they will be offering the license at this discount.