Only in constructed formats (where you build a deck out of your entire collection). In limited formats (which are hugely popular), you and people you play against build decks out of a common pool of cards. There is an entry fee and there are awards for finishing in top spots. So, in the long run, if your win rate is high enough, you can play for free or even make money, but if you suck, you're going to spend a lot.
In order to get to the cash prizes, you have to train a lot, and the price of training is high enough that you have got to resell cards to profit (although online versions made it easier to acquire draft/sealed xp).