You can study finance or actuarial science, which are "promising" subjects, but in fact, you can really choose what you like. For example, you can say that you like sta and you can do operational research. These will not make too little money.

If you want to save some money, go to America. You will have a better chance to get a scholarship from a good school. I want to go to England, IELTS 6.5 or so. If you study financial mathematics, some schools may get 7 points. If you go to America, it's about the same level.

I am not sure about the cost. In the United States and Britain, the scholarship is about 3,000 yuan, and the tuition is about11000-15000 yuan, which is related to your subject and school.