Luckily for some of us in the socialized countries of the EU, there is a court ruling that MS has to sell it's stuff to everyone for the same price.

Since MS wants to put Win10 on as many machines as possible, many OEMs or companies get the keys for free or nearly free.

You can then buy them from those OEMs (or whatever way that keys took) for cheap. You can get the Win10 Pro version for under 10€ (Home is about 25€).

It is very likely you have to use the phone activation, but after that you are... ahem... windowed :D

Of course if you don't need Win10 for whatever reason (e.g. gaming) then avoid that combined spy+adware.