I hear what you are saying. When you are coming in late from the East Coast and you are on East Coast time it can be really hard to even keep your eyes open, never mind drive for half an hour in the dark on unfamiliar roads. The last time we went my daughter was 19 at the time so not a little kid but she
fell asleep while speaking in the rental car on the way to Aulani and it was late afternoon Hawaii time. We were cracking up, it was like she was a toddler again.
I would take the time to do a price break down and figure out what is your best option.
You could rent from on site Aulani location but as you say, it is more expensive and I think you only have the option of Alamo and as
@nkereina mentions the Enterprise a couple of doors over at the Marriott.
You could also take a taxi or uber back to the airport the next day and pick up from an airport location. I know this sounds like a lot of running around but you are going to probably be up early the first day anyway. I am not sure what the average taxi cost is from Aulani to the airport but I suspect it is in the $50 range. I would determine how much you are going to save in total on your car rental and then decide if it is worth the time and hassle.
One more thought is cancelling the first night at Aulani and staying in a hotel close to the airport. I know this isnt an ideal way to start the vacation and honestly the hotels near the airport are strictly for efficiency but they have shuttles and are 5 minutes away. That way you can wake up early, go back over to the airport and head to Aulani wide awake. I would not suggest going all the way into Waikiki as a way of staying close to the airport. Waikiki is physically closer than Aulani but it is going to cost you about 2/3rds of a taxi to Aulani so there isnt much point. One caveat-I have never stayed at a hotel near the airport so I honestly do not know what they are like. I would do my due diligence by reading reviews and checking these boards for TRs etc Here are links for a couple of the hotels near the airport
https://www.bestwestern.com/en_US/b...stern-the-plaza-hotel/propertyCode.12008.html
https://www.theairporthonoluluhotel.com/