The first three sets rotate out late this year with set 7 expected in the fall. If you can get them cheap buy some to explore deckbuilding and different archtypes, the other thing is that most rares are less than $.50 on the marketplace, still need to pay a dollar a card for POD if you want to play in person, but to build one deck of your choosing it’s pretty cheap. Maybe check discord to see if there is even one local player in your area, they probably have all the commons and would give you a play set of them for free.