It doesn’t cost students and parents any more than anywhere else: the fees are the same, and in fact accommodation and living costs can be much less because of shorter terms, subsidised rent, and lots of funds available from the colleges for everything from book grants to bursaries.
In terms of “full economic costing”, however, no fees pay for the real cost of the course in any university - it always costs the university more than the fees to provide the courses, etc. Obviously, that also means the cost of libraries, buildings, salaries, all sorts of things which get cross-subsidised by universities’ endowments, conferencing businesses, catering, grant income, income from property and investments, etc. In Oxbridge those costs are even higher - estimated as over 21k per student in provision, against fees of less than half that. A lot of that is the teaching: from more lectures to the tutorial system to more staff. And a lot of it is also the cost of really amazing library and lab provision, all sorts of teaching and skills provision for students, salaries, administration, electronic resources provision, student theatres, subsidised bars and catering, the careers service, university counselling, and so on and so on.
Oxbridge tends to have more money available to cross-subsidise this because both the universities and the colleges tend to have bigger endowments and investment portfolios, as well as more grant income, largely in the sciences; more ability to fundraise from alumni, and other multiple income streams to use in subsidising student provision.
It also relies on a heck of a lot of goodwill and unpaid work from everyone who works there, from admin staff to academics to PhD students. Quite a lot of the so-called “perks” (things like subsidised lunch in college and so on) are by way of payment for a large amount of unpaid goodwill work that keeps it all going.
(On another note, my students certainly don’t wear chinos 😂 They are normally in baggy jeans, trainers and a jumper like any student these days 😂 Formals - well, they go to those because it’s an opportunity to get a nice meal and booze pretty cheaply, albeit in a Tudor hall or two. Some of them do music and theatre productions in the chapel, but then they do that in lots of places. And it’s mostly the tourists who go punting, but most students do it at least once after exams to get pissed on the river with some cheap fizz and a picnic. Why not?)