Is there any mod for it? I feel it's too easy to make money selling potions, I'd like to balance that.

Well, you could not sell them, or you could edit the game setting http://cs.elderscrolls.com/index.php?title=FPotionGoldValueMult to be 0

Alchemy Advanced. Not only is it a fantastic alchemy mod, but it has lots of customizable settings like potion value and weight.

You might also want to look at Enhanced Economy. It makes a number of changes to the way the game's economics works and includes some options for setting the prices for potions.