Don't think this is the way to go to be quite frank, the goal was never to stuff your deck with high-cost cards (which are often limited by scarcity) anyway. Cheap decks are still able to climb the ranks well, so I don't think this idea of deck ranks would work out too well and it's really coupling card strength and their prices, which isn't a good sign for something that should be game-first. Another method of separating these high-cost/low-cost decks would be to take a page from MtG/etc. and introduce different formats. e.g. Pauper mode means no epics and above, etc.