If you are looking to hire a car in Fiji, then you need to know the prices tend to be a little more expensive than you might expect. The reason for that, is the high import duty on vehicles. Prices to buy a vehicle in Fiji can be double (or more) than what you would pay for something similar in NZ or Australia. So hire companies naturally have to increase prices to cover the high costs of owning a fleet.
However, there are some discount places that will do you a good deal...if you are prepared to hire outside of the big name rental companies such as Avis, Budget, etc. I have paid as little as fj$50 a day, compared to an average of fj$100+ a day at the big places. The car may have been a little older, and most definitely 2nd or 3rd hand. But it was cheap and reliable.
Of course, you don't have the service or safeguards that you might have with Avis or Hertz, so you need to consider that. And the quality of the car may not be as high. Still, I have never had any problems myself.