Official sites like Microsoft are the safest but most expensive route.
If your hardware was previously activated, you can often reinstall Windows 10 without a key at all; it will "call home" to Microsoft and reactivate automatically. 4. Buying Windows 11 to get Windows 10 cheapest way to buy windows 10
If you want a full activation for the lowest price, third-party marketplaces often sell keys for a fraction of retail. Official sites like Microsoft are the safest but