I love Hawaii. I got married there and have visited often over the years. I have only been to Waikiki once and had fun, but I prefer quieter places so my favorites are Maui, Kauai, and Hawaii (Big Island). My brother owns a condo just south of Kona but to be honest, it's usually cheaper for me to get hotel, air and car together than to take advantage of the cheap rate he charges me. In fact, one year he gave me a week in the condo for free as a Christmas present, but when we went to get air, it was actually cheaper for us to add on 3 days at the Hilton Waikoloa with our air than to just book the air by itself!
Having a kitchen is nice, but food is very pricey. It doesn't always save you much to buy groceries over finding basic restaurant options, especially if you share. If you can, go to local farmer's markets and things like that. In Kona, for example, you can get fresh beautiful DELICIOUS pineapples for a bargain price, as well as avocados, bananas, papayas, mangoes, and many other fruits and veggies. The most expensive thing is when you stay in a pricey resort that is somewhat secluded because the options are almost all expensive. It cost $5 for half a papaya from the Hilton Waioloa snack bar, but down the road in Kona farmer's market, we'd paid that much for 10 whole papayas. Luckily, we bought one of those cheapie ice chests and brought some things with us.
I live in CA so it's not a really long flight for me and there is usually a great rate on air (though not at Christmas time!!). It's more expensive for me to go to
Disneyland than Hawaii!
I hope you have a great time! I just adore Hawaii