We used Crown for both our inter-island moves....we moved back to Auckland 3 days after the earthquake.
They were more willing to negotiate the price compared to the other moving companies that do inter-island moves.
Rail freight is the cheapest option, but has the highest risk of damage due to shunting, according to our the insurance company, so I would recommend container on a boat option if this is a concern for you.
We had moving insurance through our household insurance company as an additional short-term policy and it was way, WAY cheaper than using the shippers own policy with more comprehensive cover.
Crown also arranged for one of our cars to be freighted up to Auckland.
It took 2 days total and we filled it will all our garden pot plants and my worm farm since we didn't want those in the container with our furniture.
I think the total cost was around $700 door to door including insurance....which wasn't too bad when you consider we would have needed to pay inter-islander ferry, fuel and at least one nights accommodation if we'd have driven the car up ourselves.
There are other smaller companies out there, such as Canterbury Bulk, that work out cheaper if you are prepared to self pack a container or lorry within a 2 hour time slot (not long) between them dropping off and picking up....
you pay by the hour if you go over this time.
However unless you have several strapping men ready to pack up, you'll end up needing to hire someone for this job as well as completely pack up your belongings which means you'll have to buy packing materials yourself.
We decided for $500 total savings it wasn't worth the hassle and hard work involved.