I can’t answer for Oxford, but being as I went to Cambridge I’ll give it a stab.
Tuition fees when I went were approximately £1,000/year for all subjects, and my living expenses were approximately £3000/year. There are very cheap loans available to all to cover this.
Tuition fees are increasing to up to £3,000/year (see link), but this is not paid for up front but as a low interest loan payable once you start earning above a certain level (IIRC it’s something like 5% of any income above £19,000/year).
I figure that four years at Cambridge cost me something like £18,000. My starting salary was £21,000 which is probably a bit below average (engineers in the UK aren’t very well paid compared to some other professions).
It should also be noted that to date (I left 3 years ago) I’ve only paid back about £3,000 of the cost of university - at the current rate I’ll be nearly 60 by the time I finish paying for it!