The meta we had last season was also pretty fast and we have an expansion dropping next week. This means that you'll have a ton of people experimenting with the new cards and also a ton of aggro feasting on unrefined lists.

The game is extremely generous and you can get by without paying for cards, making a solid tier 2/tier 1 deck should take probably 3 weeks+, less if you're going for decks that contains the free cards you're given at the start. It gets faster from there.

Your main goals at the start should be grinding your Weekly Vaults to at least 10+ and clearing region rewards every 4 levels to get wildcards. These are used to unlock a card of your choosing.

If you're going to pay for a deck, the most expensive deck full of epics and 6 champions should set you back $69 but that's if it contains champions you don't own plus most decks don't really use that much epics. Expect the price to be way less if you're considering paying for a deck.