First, the estimate for $100,000,000 from 24,000 people is WAY overstated. That's nearly $4,200 per person. NO WAY.
Yes, Hawaii is expensive. But as mentioned this is the off season. Take a quick look at Travelocity, Expedia or some other travel site and you will see the most expensive rooms listed this time of the year are about $250/night per room. That was the Marriot on the beach. Most other major hotels like Holiday Inn were listed for half that much. Rental cars, with tax, are about $225/week. Food, well, I can't think that on average, a typical couple is going to spend more than $100-150/day on food.
I would estimate a 10 day trip at about $4,000 for a couple, less than half of $8,400 ($4,200x2) that is being estimated. I would think that about 10 days would be the average; some staying a week or less, others staying two weeks or so. Plus, the 24,000 number would include some children that would further reduce the overall amount spent (staying in same room as parents, not eating as much, etc).
I'm just not sure how they came up with such a high number.
Rub a Dub