Why not compare the annual rainfall in Cambridgeshire, Oxford, or London vs New South Wales? You might be surprised.
Coventry (home to Warwick) is rainier than those three UK regions, but still drier than NSW. So is Edinburgh, home to another strong university.
All the UK schools will be much cheaper than the US ones while giving you a comparable if not superior math education, unless you can get permission from the US school to skip prerequisites and start with more advanced courses freshman year. Without that, among the US universities I think UWisc or UIUC would have the best undergrad options for you.
Can you explain what you mean by having no time for SAT/ACT?