Delta allows you to pay incrementally with miles, i.e. there is an option at check-out to pay with miles at a conversion rate of 5,000 miles = $50. It's not a fantastic conversion rate, but it's allows people with lower balances to use their miles more efficiently.
Hilton Waikoloa Village starts at 50,000 points per night. Again, Hilton allows you to pay with cash and points, so there's likely a sweet spot that'll allow you to maximize the benefit of those HHonors points. HWV is a nice spot for a family, but there are a ton of other options nearby.
We thoroughly enjoyed our week at HWV a couple of years ago. The Big Island is fantastic, especially when you get out an explore. We only spent 1 full day without leaving the HWV property, the rest of our days were spent at Volcano National Park, Mauna Kea Observatory, Hilo, Kailua-Kona, Waimea, Waipio Valley, etc.