In which environment?
Many years ago, Wizards of the Coast realized that the game was unapproachable when all the cards are legal. So they created supported formats, and people just agree on which one to use before they play. For instance, we could play a deck where all cards have been printed in the last couple of years (the standard format), or we could play only with common cards, but from any expansion ever (pauper). The formats where you can play with pretty much every card ever printed are not those most, if anyone, play.
Owning four copies of the cards in Standard is pretty expensive: A refresh is about a grand a year. But even pro players don't do that. People aim for having a couple of decks per format, Which is a lot cheaper, especially if you trade your unused cards.
To play for cheap, people play draft. 8 people, 3 boosters per player ($15 or so), and you can have a little tournament for a few hours. And enough drafting will get you cards that you could save to use for standard decks.
It's still a pretty expensive hobby, but it's not like you need to buy the $1000 cards to play.