Each Hawaiian Island has its own appeal, and has enough happening to fill your vacation days very well. When I said don't waste tiime going to Maui, it was in response to you saying you were staying on Oahu and Kauai. Going to Maui for only a day or two does no justice to Maui, and it adds to the stress of you trying to locate a place to stay in between those other island stays.
Yes, interisland flights are usually less that $100, so your pricing is right. Don't forget to factor in a rental car, the time and costs of checked baggage, buying groceries on that other island (assuming a timeshare stay) and other costs that are miltiplied by however many islands you intend to visit. Don't forget to include the return interisland trip, too - those planes fly in both directions.
I used to live in Hawaii as a teenager, and I've traveled back there dozens of times since. I love each of the islands, for their individual charm, and the things that make each one worth seeing. That said, when I'm booking a Hawaiian vacation, it normally includes one week each on two islands. I fly into one, spend my week (or whatever time) there, then hop to the other island, spend time there, and fly home from that island. Each island has flights to and from the Mainland.
Don't muddy the works by trying to do too much too fast. You can't see everything in Hawaii on any length of vacation, so don't try. Book what you can, enjoy the heck out of it, and fly home, knowing you'll soon be planning another trip back to the Islands to see what you didn't see this time. It gets under your skin, and you will never be the same.
Aloha,
Dave
