I have the Core Set and I'm struggling to figure out where to go from there to expand my selection of cards. Ideally I'd just buy all of the expansions but that's not something I can afford. Assuming I'm not bothered about getting any of the non-Core Set mages, and that I just want access to cards I don't get in the Core Set, what is the best way to about it? Does every expansion have cards unique to it or do they get duplicated in other sets?