Having visited the Big Island several times, I can offer some advice:

As you know, I believe that you can get some great deals on upscale resorts in Kohala coast right now on Priceline - as you can almost certainly get either the Marriott or the Hilton in Waikoloa, or the Hapuna Prince for bids of between $105 and $125 a night. But, with the cost of dining and possible resort fees on top of that, these places perhaps might still be beyond your budget - Plus, the Kohala coast is as far as you could get from hawaii Volcanos National Park.

If you want budget, there are lots of places in Kona that could probably be had for under $100 a night that are not too bad - but these inexpensive places in Kona are a much less luxurious, and overall much different experience than the luxury places on the Kohala coast offer.

One other possibility would be to stay at a B&B somewhere further south, like the Captain Cook area. These are all small establishments which vary widely, but many are very nice and fine values Another advantage of these is that they are near Kealakakua Bay and Place of Refuge - two of the best snorkeling sites in the Big Island - and they are only around a 2.5 hour drive to Volcano, whereas the northern part of the Kohala coast is more like 4 hours.

A couple of specific recommendations: In Volcano, I really like "My Island Bed & Breakfast" It's inexpensive, and it's lovely.

http://myislandinnhawaii.com/index.htm

And when driving to or from Kona to Volcano, be sure to stop at the black sand beach in Punalu'u - about an hour or so south of Volcano. It's a really special place, and it's loaded with sea turtles.