For me, i have invested €100 in packs when the game was still in Beta. And i got enough wildcards to be able to build multiple decks over the past year in combination with wat i got from free packs. I think the 100 gave me around 15 to 20 rare wild cards and around 6 mythic rares plus the 90 rare or mythics that are in every pack. now i just go with the season pass wich gives me enough to keep up.

But i here people doing it without paying for everything. So it dependance on how dedicated you are to getting your 10 to 15 wins everyday.

I could suggesd spending money 1 time as you would pay for a normal game. Doend that money on building a strong meta deck like agro red or white. Than use that deck to grind for gold