In reply to pancakeandchips:
It looked like you can turn up at camp 4 without a reservation for first come first serve spots when I checked the other day. When you queue just say how long you want to stay for, the rangers are generally pretty accommodating.
You can stay at backpackers the night before and and after a bigwall using a big wall (easy to get) or wilderness permit (harder to get), but it's a similar price to camp 4 and a bit faffier (but a good option of nothing else works).
Post edited at 07:45