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Yeah, Cambridge is pretty expensive. (I think the best US universities are a lot worse, but haven't actually looked at the numbers. Some or all of these places may have some kind of assistance available if you're very poor or very good or both.) The recent reduction in the value of the pound (because of all the "Brexit" hoohah) has made UK universities a bit cheaper for foreign students.
I'd hesitate to call anything universal, but I'd consider at least the following things. You've probably thought of them all already :-). Some of them are awfully hard to assess. You may be able to get useful answers to some of them from the universities themselves, though of course it may be in their interests to mislead you or to refuse to answer some kinds of question.