Prepping own meals in Hawaii is not all it's cracked up to be. Food is expensive and because you are only there a few days you will have lots of waste. Yes you can shop at Costco, but it's still expensive. You can go eat at budget options in Kihei (Maui Taco etc) for not that much more. Being oceanside is a big plus, you probably won't be back in Hawaii for a few years.