It's really not too much grinding. I can get about 4-6 upgrades an hour if I really try. I agree with other posters that the price should be based on the card.
So if you want to try a new upgraded 30 card deck with new cards, you need to grind for 5-6 hours non-stop? You don't think that is too much?
This card collecting and rare hunting is a big part of CCG's like MtG, but the difference is that they are in it for the MONEY. Elements however is a FREE game so there shouldn't be any grinding. This whole grinding crap was invented in MMO's because developers couldn't design enough content and they had to force players to grind. Somehow this mentality of "it's ok to grind" has been adopted by the gaming community.
If I had my way, there would be no money, no rare cards, or no grinding. We could have a system where you would "unlock" cards, and once you've unlocked one of them, you can use as many as you like in your deck.
This game should be about building different decks, not grinding money to buy cards.
Yes, I actually DO think the grind should be 4-5 hours. Heck, maybe even longer. I play A LOT of Fire Emblem: DS online, and let me tell you, to make a competitive team, you have to spend hours upon hours of clock abusing or rng abusing to get max stats. Not to mention the hours of arena abuse for money to forge good weapons, and the weeks you have to wait to get brave weapons from the online store (each brave is only available for one weekend a month). I would say that I have 3 competitive teams online, and each of them probably took upwards of 70 hours to make. So no, a 4-5 hour grind is NOT too much.
Though in my system, if upgrades were based on the card, it wouldn't take 4-5 hours. Some cards, such as pillars, should only cost 1000 to upgrade, but others, like Pulverizor (which has an amazing upgrade), should cost 2000. So the grind would depend on which cards you were using.
A problem with your idea (I saw your post farther down, too) is that many noobs would quit early because they wouldn't be able to unlock the first card, as the starter decks generally suck. Unless you had a list or something of which cards were harder to unlock and such.
Also, using as many as you want would be REALLY cheap. Here's what I would do:
-Get starter poison
-Unlock the card "Poison" if needed
-Deck: 20x poison, 10x bone pillar
Obviously, no card limit would make the game even MORE unvaried, and if you HAD a card limit with your system getting started would be VERY slow. There would also be very little replayability once you unlocked all the cards.