It sucks, but there's nothing you can do about it. Argentina has been lucky in attracting lots of visitors without trying since their currency crash earlier this decade, so they don't care how much you get soaked on flights. It's mostly a monopoly airline situation except for a few small ones that come and go but mostly operate down there during high season. (Jan-Feb.) A local agent might know the options for those, but otherwise your only choice is to take some long bus rides. Some of those are sleepers, so it could be worth it.