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.
It's perceptually free if you bought it with your PC. And it's actually free if you took advantage of the free upgrade offer.
I've picked up a few licenses off MacHeist for like $10