In the past two weeks, Cheapflights users have found many deals under S$ 86/day when booking a rental car in Oahu. The absolute best deal a user found was for S$ 64/day from Economy Rent a Car, booked on Jul. 28.
Generally, for a better deal it’s recommended to book in a timely manner (to save up to 8%). Cheapflights recommends you book around 12 days prior to your deserved date. Booking as early as you can also increases the likelihood that you’ll get the ideal car.
Typically, how long you can rent a car for depends on the inventory of the supplier. For Oahu however, it is certainly possible to rent a car for an entire month.