The cost is rolled into your PC when you buy it. Its not free.
Your $10 licenses are not legal. Sorry. Those are sketchy grey market keys. Though Microsoft likely won't go after you for it, so I'm not sure it matters.
You should have just saved the $10 and downloaded a cracked copy.
Cracked copy = trusting some shady 3rd party
If they're authenticated when I install the OS, what makes them illegal?
You’d rather have an unofficial ISO?
Why?
I'm not going to switch to piracy to avoid some gray market sketchiness, as long as the keys don't seem to be stolen.