That's why there are people in legendary rank that have never spent a penny outside of an arena run or two, this is a completely free game with the choice of skipping the grind with money for those who value time over money.
RNG, well that's a rather laughable concept to complain about. Having played other card games like magic, yugioh, pokemon, etc. I can say with a fair amount of confidence this game has less RNG bullshit than them.
You can only have 30 cards in a deck meaning that your chances of drawing a useful card is a higher percentage than most TCG's.
Due to the lack of land/mana cards (replaced with mana crystals per turn) there is no mana screwed situations, rather the worst that can happen if you built a deck with too many high cost cards.
Honestly though Hearthstone is a card game, complaining about RNG is like complaining that the sky is blue...