Take a quick flight to the big island instead. You won't regret it, much more friendly and less of a tourist gouge than Oahu. Great bouldering on 5-10 m overhanging basalt cliffs out of the sea at South Point. Climb, fall off, repeat. Best on a calm day, unless you're a confident swimmer. There used to be a ricketty ladder to get out, but I think it's gone now, so it might be a good idea to anchor a rope up top so you can prussik out. You might meet some locals there who can advise on other spots. Google "bouldering hawaii big island" for more. I don't know any of the other sites. There is good camping (or you can rent a rudimentary cabin) at Namakani Paio near Kilauea crater. There are other little-known campgrounds scattered about, some you can only reserve from on the island. Otherwise good friendly hotels at Hilo and Captain Cook (keep away from Kona, a major tourist trap). Good walking up Mauna Loa or along the Kau Desert coast. There are some great secluded ocean beaches hidden away along the southwest coast, though totally different from the white-sand beaches of Oahu. Plus you get an active volcanic eruption (http://hvo.wr.usgs.gov/activity/kilaueastatus.php). If the flows near Kalapana are active, hike out before dawn to take a look before the policeman comes on shift.