Let me tell you that this kinda sucks for quite alot of people. Who seriously can compete in a tournament where you can change decks every match and upped cards are allowed?
People with more than one deck and (optionally) some unupped cards.
I know it seems daunting at first, with that first little set of cards. Seems like money is scarce and even one upped card is an impossible goal that will take days of grinding on the AI to attain. The truth is not so oppressive though. There are a handful of unupped decks that can reliably beat some of the AI6 decks. You'll maybe win 1 out of every 5, but selling an upped card from the AI6 (or if you're lucky, two or three) nets you a little over 1100 electrum-- what would take hours grinding on AI3 on dozens of games.
Get an unupped godkiller deck, earn some money. Start working towards a more efficient upped godkiller. Once you're there, money is no issue. I went from having nothing to over 600 cards (with about 100 upped) in a month of very casual play. I might play a few nights a week for no more than an hour. In that small amount of time I went from being a total scrub, wondering how the hell I'm ever going to play in tournaments (where you are) to playing on even keel with the tournament vets.
It's a fairly short road from nothing to swimming in electrum. The longest stretch is getting from the starting deck to a godkiller deck and building an upped godkiller. So you can set your sights on that and aim to be a viable tournament player, or you can choose to stay where you are and place the responsibility of your lack of accomplishment in the game at the feet of those who are not responsible for it.
The tools are there for you to reach the plateau you seek. Seize them.