Difference between cheap stand mixer and expensive kitchenaid one?

Power and durability, basically. Buy a Kitchenaid and you'll probably never buy another mixer no matter what you use it for. But if you really do only use it rarely and only make cakes, the $50 one might last you quite a while. I suspect a cheaper mixer wouldn't stand up to much breadmaking even if it does come with a dough hook. I don't even think I'd bother with a stand mixer for the occasional cake, actually. They take up a fair amount of room and a handheld mixer will make cakes, whip cream, beat eggs or make icing perfectly well and take up a lot less space. I have one that even came in a neat little case so it stores very tidily.