I mentioned before that you can legally purchase W 10 PRO @ 11 PRO (can't remember if it was on this thread) for under $50 (I had bought BOTH for about $39 each) on Kinguin.
I just took this screen-cap from Kinguin, and it is even cheaper than what I had bought them for back then:

Totally legal.. What they do is take overstock software from companies that aren't using it and resell it at discount prices. (There are 2 companies I purchase software like that).
(And, like you mentioned, the PRO version gives you more options, which is why I purchased it for both versions.)