Think it depends though. King's halls are about the same price as intercollegiate halls.
I was at Nutford for my first year, and that was bout 500 more than Wolfson (the most comparable hall I suppose, since its non-ensuite and single) for the whole year. Definitely works out cheaper that way.
Downside is that if you don't want to/can't eat at halls (which happens fairly often) you're essentially paying for nothing. They did give packed dinners (sandwich, juice, fruit and some form of biscuits) but it wasn't worth it.
That was 3 years ago tho.
Edit: looks like Nutford's single rooms are still bout the same price as Wolfson's and bout 10 more than EwenHenderson. So... yeah.