I studied for 2 years in the US, in San Jose, California, so I can share some info your DS will need.
The colleges he is looking at will have an international student team. He should make contact with them and ask their advice about the process, costs, accommodation options etc. They are the experts on this stuff, and they will always be helpful.
He will pay international student rate or 'non resident' rate, not the US 'in state' student rate for his tuition. For somewhere like San Diego State, that will work out at around $50,000 per year, and the degree will be a four year degree. There will be other costs he will have to pay on top of that, such as books, health insurance, visa, general living expenses etc. It will likely be broken down on a per semester basis, so payable at the beginning of each semester.
sacd.sdsu.edu/financial-aid/financial-aid/eligibility/cost-of-attendance/cost-of-attendance-tables/undergraduate-non-resident
He will need an F1 student visa, for which he will have to visit a US embassy to apply in person once he's been offered a place (or at least that was the case pre Covid). He will also have to cover the cost of this. If he doesn't have a passport, or it's due to run out before the course starts, it will need renewing before he goes to the embassy appointment, as he will have to hand it over as part of the application. He will likely have to be able to prove how he will afford the cost of the whole degree during that appointment, or they may not approve the visa.
The visa will have restrictions on what he can do employment wise. In the first year of his degree he will only be able to work on campus, and after that he may be able to find work off campus only if he is in severe hardship, or if he is doing something related to his course. There will be varying amounts of work on campus, for somewhere like San Diego state there will be loads of cafes, shops, food halls etc. But there will be lots of competing people too, so it's best to assume he will not find work in the first year and plan accordingly. In his second year onwards, his course department might be able to help him find work, but again it's not a given.
Some universities insist first years live on campus, some insist international students live on campus for the whole of their course. He should check the rules for his chosen course/uni.
He will not be entitled to a standard UK student loan, or a government backed US student loan. There are private US and UK based companies who do student loans for international students, but I would recommend getting some serious financial advice before going down that road. He may be entitled to a bursary, scholarship or grant. The university can support him with applying for grants or awards that international students would be eligible for, but they can be very competitive, and shouldn't be relied upon until they are actually offered. There also may be charities and organisations in the UK who sponsor students to study abroad. He should get googling now on that.
He may have to take some academic assessments in basic stuff like maths and english, and he will also be required to study a range of classes not related to his major subject. That to me was one of the big appeals of a US style degree, it allowed me to study a broad range of things I wouldn't have necessarily covered in the UK.
My US study experience was amazing, and I would absolutely do it again. I learned so much outside of my academic programme, there were tonnes of student associations, so much going on on campus, and I would go back and do it again in a heartbeat.