It is generally expensive and you will be not within easy walk of cheap food on the other end of the North Shore. There are many inexpensive GREAT places to eat in Hawaii in general.
Here is a tip you might like and you might not. I do it a lot. (My daughter and I stayed in Beverly Hills this past summer and did it almost everyday because she was recovering in a hotel room)
Call a restaurant, order whatever you want, and then call a cab to pick it up. (Order someplace 5-8 dollars away) You only get charged for the one way fare, which is often less than delivery fees. Most of them don't mind at all and some places will accept a credit card over the phone, ask to speak to the manager, etc. Sometimes the cabbie just puts it on my bill. Make it easy for him and meet him on time, etc. If you find a driver that you like, just call him each time and that way you don't have to re-invent the wheel each time. JB and I even did this in Palau, when we were lazy after diving all day. Indian, Italian, you name it!
Also, I take everything out of the honor bar and put my OJ and coffee cream in there along with my leftovers from the night before.
On the North Shore, ask if places will deliver for you and eat it at the pool.
Lots of fish sandwich places, Mexican, etc at the other end of Haliewa! Turtle Bay food is kinda average, but the hotel is really nice. I love food, so I don't mind making some effort to get what I want. OH...and go to the store and buy some nice wine for your room. Almost everybody I know does this now. I can great a good bottle for 15 dollars or pay 8 dollars a glass for something I don't even like.
My favorite place up there is Kua Aina, and I like the ahi sandwich with avacado. Also, Halaiewa Joe's and Jameson's. You could make a deal for the multiple days and prepay even.
(We recently rented road bikes on Maui and made some tracks to much more of Lahaina than we would have walking.)
Aloha