Hi Dave
Yeah, you're not too far out at £11,000. I went to Oxford and I would guestimate that I was closer to £13,000 for living expenses.
I was paying £400/month rent (but not living in halls). This got me a flatshare within the Oxford area (nearer the city centre than the airport but travel to and from the airport was always opposite to the direction of congested traffic - so I was no more than a 15 minute drive away).
I'm not sure how much the quality of the halls has changed at Langford Hall but while I was there, there wasn't a kitchen area to prepare food so you were forced to eat in the canteen which wasn't cheap.
In these living expenses included an extra hour of tuition the US and a retake of my partially-passed 170A.
I also went a tad over the top in the US with visits to various places (Vegas being a notable example.... twice).
....oh and I hired a car out there as well for a few weeks. A big fat Mustang. Couldn't help myself.
Best of luck with the budget.