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.

• How well do the courses available match what I am actually interested in learning?
• What possible career paths might I follow, and will going [wherever] and studying [whatever] help with them? (Be realistic!)
• Will I enjoy my time there? (This depends on things like climate, culture, difficulty of course, interestingness of course, other people there, ...)
• Will I meet plenty of people who will be friends, mentors, useful future contacts, etc.? (How much this matters, and how much use you can make of the meeting-people opportunities, depends on your goals, personality, etc.)
• Will my having gone there impress people? Will I care?
• Will the academic work be too easy or too difficult for me?
• Is it assessed in ways I can do well at? (I'm not sure how much this varies. But e.g. there may be variation in whether it's only your final year's examinations that count; in whether there's coursework as well as examinations; in whether some examinations are "open book".)
• How much will it cost? (Take into account any scholarships, bursaries, loans, etc., available to you.)
• If while there I find that I want to be doing something else, how flexible will they be? (At some universities, perhaps all, it's pretty easy to change subjects, at least if you're moving from a "harder" to an "easier" subject.)
• Will they actually have me? If it's uncertain, am I giving up better opportunities by trying?
• If the university is abroad, will I face prejudice from the locals? Or feel prejudice myself against the locals? How comfortable am I in the local language? How comfortable am I with the local culture? Will the food etc. be OK for me?
• How do they teach? What's the actual quality of teaching like? Will I be being taught by world expert researchers or struggling graduate students? (Note: the former are not necessarily better teachers.)