Yes, you can purchase Windows 7 at a lower price and then upgrade to Windows 10.
Yes, you can purchase Windows 7 at a lower price and then upgrade to Windows 10.
You can purchase a Win 10 copy for $20. I think Paulshardware has a video about this. You might also try using Windows 7, 8, or 8.1 on a Windows 10 installation. If that doesn’t work, contact Microsoft. When I upgraded after the release of Windows 10, my key wouldn’t activate and they provided me with a new one.