In reply to johnmctighe:
You can probably do without a car in rjukan. Most routes you can take the bus to, hitch or even walk. And I don't imagine it would be hard to get to the town without one.
Of course it is more convenient to have a car, but if you want to sacrifice some freedom, exclude some areas and allow for a bit more time getting to and from, you can save quite a bit of money while still getting most of the experience.
I live in Sweden so for me the most economical/practical way is just to drive there, so I don't really know personally.