New Zealand - Rental Car

How are fuel prices in NZ at the moment? Given the increase of fuel cost in Australia, I’m guessing NZ would be even worse? We’re paying about $2 per litre. I’m heading to South Island in early December and are deciding whether a car is worth it ($600) with the increasing cost of fuel as well. We have about 10 days to explore from Christchurch to Queenstown and then we fly domestic back to Christchurch and then to Perth the next day. Is there a cheaper way I could explore? It doesn’t look like there’s good public transport outside of the major cities?