Every so often I get a nice temptation to get into MTG, though due to my crazy schedule it's always tempting to go online... As part of that look I found a nice little guide for the prices you can expect for competitive decks, that also includes other games: https://www.mtggoldfish.com/articles/how-expensive-is-magic-online
For the interesting part for TLDR-ers
MTGO: about half of what paper cards costs (but still $100, to $X,XXX). With some fun options for cheaper decks and play styles (unofficial penny dreadful touries, official pauper play styles, and just playing with people that are sane).
Pokemon Online: Too contorted to easily measure, but likely cheapest.
I guess that explains why companies were so fast to try to spam their own card game, that even when Valve wasn't bothering to make games they managed to find the muster to announce their own card game. Since you'll end up with two types of players, those that "play forever" to get their unlocks (not an option for MTGO) and those that pay the price of two to three games for your one game.
While these games do play at "MMO scale", I wish someone would release an actual MMORPG that offers the complexity/thoughtfulness of a cardgame for their combat. Not everything needs to be designed for looking good with particle effects and twitchy gameplay.
Practice doesn't make perfect, practice makes permanent.
"At one point technology meant making tech that could get to the moon, now it means making tech that could get you a taxi."