My Wife and I went 2 years ago. Now... we are cheap. So we stayed in the cheapest hotels, rented a car, ate at local diners and stuff like that. But it was the best time I have ever had.
First of all, we went in the winter right after Christmas. We also went to the big island, which is probably the least "touristy" of the Hawaiians ( at least that what locals told us) The temp is 75-80 year round' so winter, summer...doesn't matter but it is a lot cheaper and there are a lot less people.
The big island has diverse weather. The Hilo side is very, very wet. It rained most of the time. The other side- the Kona side- is drier and a bit warmer. We actually stayed in Captain Cook, which is above Kona. The cool thing about it is that Captain Cook is near all the Kona Coffee plantations so you can see that. There's also a few snorkeling places off the beaten path, namely a place called " The place of refuge" . The water is warm and salty so you can just lay in the water all day and you'll float like a cork. We bought shitty masks and snorkels at the hardware store for $5 and they worked great.
We stayed at an old hotel called the Manago. here's the site: http://www.managohotel.com/
It was around $65 a night. The food there was super good. No- it isn't fancy. But its more authentic. There are no TV sets. But the balconys look out over the water.
Let me put it this way: We had very good food, met some really nice people, even made some friends we had beer with. On the other hand we went down to some of the "Touristy" hotels that had tiki torches, lagoon pools, and private beaches. I almost felt sorry for those who stayed there. It was so fake and ridiculous. The people who stayed there I doubt actually left the resort.
lastly- go to the KTA. Its a chain of grocery stores there and the food there is great. Ahi Tuna is dirt-cheap in hawaii so if you can find yourself a park with a BBQ grill, you can have ahi tuna for about $5 apiece.