There are a few misunderstandings here.
The first is the cost thing. Financial aid and scholarships are two different entities. The first is basically a waiver, or a write-off, and perhaps loans from the institution itself. International students are eligible for needs blind admission and full demonstrated financial need covered at a select few universities and liberal arts colleges. Scholarships are specific funds offered by organisations to specific categories of students.
Your annual bill will include tuition plus room and board plus any miscellaneous fees.
In the US, you can enjoy a much higher starting salary than you would in the UK with just an undergrad degree under your belt. Engineers are particularly well paid, and finance majors are too.
Graduate school includes medical school (four years, followed by residency) as well as MBA courses, Masters in Finance, law school, midwifery, masters degrees in various humanities and arts areas, Masters in Education, and PhDs. A PhD can take four to seven years. It's not a one size fits all proposition.