Unity does have great 2D support as you can see with many games in stores (thomas was alone, i believe Hearthstone, broforce and more).
Also yes, the Unity license is quite expensive But you can use the free version for any game really and sell it, unless I believe you make like $100,000 then you need to buy the full version.
Sorry if my explanation is vague, I bet more people will be able to explain it a bit better