In reply to Euan McKendrick:
We stayed at a fairly generic, fairly central hotel in Oslo, a three person room was about £35 or £40 each per night.
Imagine a premier inn standard, breakfast included too.
as for Rjukan; I can definitely recommend Sandviken Campsite, get yourself booked into one of the wooden huts they have. Make sure you ask for one with a toilet in it.
Stunning views over a lake to wake up to every morning.
Very clean and modern shower block (free to use) and sauna (small charge) on the campsite too.
It’s about fifteen/ twenty minutes drive out of the Rjukan, but we were glad of it, getting back out of the valley and into some sunshine every afternoon was surprisingly uplifting.
As for ice screws; the more the merrier, you’re bound to blunt one going into stone, drop/lose some. So don’t be shy and take plenty.
As said by the previous poster, it is expensive, you have been warned.
JRJG