It's true that 60% are from state schools, however most people definitely do not sound as if they do not have money i.e do not have regional accents, just one similar accent. Obviously there are a lot of foreign students, something like 30%, and whilst these people may often be wealthy, you must also consider that to go to a private university in the U.S like Brown or Yale you must pay very high fees and the amount of debt Americans expect to come out of university with is higher, and there is more of a culture of saving for university over there.
Although rents are relatively expensive compared to say Leeds or Sheffield, they are cheaper than London. As for Edinburgh, I've been to both Edinburgh and St Andrews' open days and having stayed in both places can say that per week Edinburgh may be a little cheaper. However, St Andrews is quite rare in that most of the private rentals only have 9 or 10 month leases so you must find a job or go stay with parents or whatever in the summer, consequently rents are slightly cheaper than Edinburgh.
As for jobs, although it is a small place there are a few shops and many people choose not to work because they don't have to or they choose to work in the summer. When I was there plenty of shops were hiring, much more than when I went to Edinburgh.
BTW I attend a state school and my mother earns next to nothing. :-)