From what I can tell, if you were to sell a $5 game made with Unity and made $200,000 per year, the total charge would be $8,000. But that charge would be $40k if your game was only $1 and $800 if your game sold for $50. For Unity Pro if you made $10 million selling 1 million copies you would be charged $60,000. That same studio making $10 million on a game written with Unreal Engine would be charged $500,000 in royalties. That is far more than $60k for Unity. It still appears that Unity is the budget option, it just isn't quite as cheap as it used to be... So I couldn't find a situation where is cheaper to go with unreal (5% revenue share) than with Unity...