Be careful about "cheap" car rentals in Hawaii. I reserved a car two days in advance from Thrifty's in the Ilikai Hotel. I asked for a car with a trunk as I'd be carrying all my luggage for the day. My request was ignored; I was given an SUV but it had tinted glass so I didn't mind. I asked for a child seat but they forgot, so I had to drive back and pick it up; Not a big hassle. But my big complaint was the car only had half a tank of gas when I picked it up. When I returned it, I put in gas back to half a tank. but they expected me to fill their tank to full. My contract clearly said "outgoing fuel level as Half" so why should I fill it up for them? When I showed the contract, they printed up a new contract which had mysteriously changed to "Full". They waived the charge only after I raised my voice.
The cost was $34 + $12 for child seat and $30 surcharge for returning to the airport.