If you're looking for cheap flights, I recommend checking the websites Expedia and Google Flights and turning on notifications/updates to receive an email every time the prices drop.

Chances are flights will not get too much cheaper after October and November. That being said, sometimes they do on a whim. Flying ON Christmas Day is always cheaper than before and after (yep it sucks but I thought you'd like to know).

AirBnB:

There are a plethora of homes for rent in Laie and North Shore, but sometimes it can be hard to find them listed on AirBnB. I recommend finding one and reaching out to ask for a shorter stay time rather than the automatic 30-60 day mandated period. (the laws around AirBnB are different in Hawaii due to Hotels)

Hotels:

There are 2 hotels on the north side of the island, one is affordable, and the other will blow your socks off. The one in Laie is a Courtyard Marriott (affordable), and the one in Kahuku is the Ritz-Carlton, Turtle Bay (goodbye wallet).

There are other options in Honolulu about an hour away that are also beautiful, and the hour drive to Laie is one of the most beautiful you'll ever see so it's not too bad to stay in the city if you'd prefer that.

In Laie we have a pricey small local grocery store called Foodland. In Hauula (5 mins away) we have a Longs Drugs (CVS) and Tamuras (small and pricey).

If you stop at Costco or Sam's Club on the way from the airport to your accommodations you can get much better priced groceries! This is what my relatives usually do when they visit. Costco and Sam's Club are about an hour away from Laie, so usually my family only takes that trip to stock up once or twice a month.