PoE is free because of selling cosmetic items. There is no selling user data. I'm not even sure what kind of data a game would have to sell about it's users anyway.
Of course, I’d be remiss to point out that you really need to shell out to get enough stash space to prevent frustration. One of the $60 supporter packs will get you just enough points and also give an alternate look if you need it. But for the same amount of money as a retail game you get a lot of content.