Looking for flight/condo deal to Hawaii from NYC

Your dates are coming up quickly. If you are going in the later half of september you are in luck as it tends to be a slower period by Hawaii standards. Have you looked into www.vrbo.com ? Budget areas of Maui will be Kihei and Napili Bay. Personally I prefer the West Side of Maui (where Napili is located). I've seen condos between $80-$110/night in Kihei. Napili starting around $100/night.

As for the Big Island you will likely want to be in the South Kohala Coast region. This is where the beaches are and you pretty much have sun all day long. The wind really kicks up here so be aware of that, but it is a good thing because it keeps the skies clear and vog free. Cheapest condos I have seen on the Big Island are $120/night or so.

If you decide on Kauai then September is a great time to visit the North Shore. Unfortunately I am not well versed on the North Shore of Kauai. I do know the South Shore pretty well though. I stayed at the Kiahuna Plantation 3 years ago for my honeymoon in a beautifully renovated 1br condo. It was around $160/night.