Not necessarily variants or misprints, but many old powerful cards are extremely expensive. By this point the volume is much lower just due to time, but many cards from the first ~4 sets are worth hundreds to hundreds of thousands of dollars depending on the card and condition.

No, but they are from the first couple sets when production runs were smaller. WotC has made a promise to the community that they will never reprint (tournament legal versions of) some of those early cards which helps keeps them rare and expensive.

You wouldn't really want those cards reprinted anyways. They're very overpowered and seem like amateur design if you look at them through a lens of the rest of MTG design history.

You may be thinking of the different border on cards from the alpha and beta sets as variants. But that's the way every card was printed back then.