Okay, Let me ease it for you.
When he eventually does apply to university, advise him to apply to Oxbridge but also to some closer universities e.g. Queen's University Belfast or maybe even areas with a low cost of living (typically northern UK)
Maintenance loans are a great tool to help him survive but given that he is intelligent and has high aspirations, I think he could potentially get a part-time job through uni related to his chosen uni course so that could aid him in cost of living and instead of doing a 52 week tenancy in accommodation, he could do a 40 week and go home for the holidays.
The government offers student loans for university degrees and maintenance loans for living expenses whilst the student is at university.
The standard is that when he starts to receive offers on UCAS, the UCAS hub will show accommodation properties and he can browse them through there and he might be able to if he ever decides to go to an open day.
I can only imagine the worry but this is coming from a person with parents who don't want them leave the city - I wouldn't worry until the time comes and I wouldn't worry - in todays government, there is a lot of financial aid and given that your son appears to be intelligent, he can apply for/get scholarships and grants for living costs or even to pay his tuition fees so he may be well off.
The costs of attending Oxbridge depends on the student, some students use online resources (which tend to be cheaper) and some use physical, some use technological devices and some don't - it really is a spectrum.
Hope this helps and feel free to ask any more questions!