Since you mentioned liking Bonaire diving, I'd highly recommend the Big Island. I've been to Bonaire 5 times, and am making my third trip to the Big Island. The shore diving is similar in many respects: you rent an SUV or truck, dive mainly on the western side of the island, which is dry and gets not much runoff; there are some rocky entries, some sandy ones, and if the surf is picking up at one site, you go look for a more protected site. My favorite sites so far are (1) Alua Beach (tiger sharks, eagle rays, dolphins, every kind of eel imaginable), (2) Puako (turtle cleaning stations, and (3) Milolli (healthy/dense coral, by Hawaiian standards). I definitely also recommend the manta night dive and the blackwater dives, which are the only dives that really do require a boat.
One thing you'll find about Hawaii diving is that it's easier to spot critters, large and small, because much of the bottom is black lava, and colorful animals tend to stand out much more.
Lots of Airbnb options in the Kona area; the condos are a little dated decor wise, with Hawaiian type fabrics that scream 1970s, but the Big Island and Kona in particular are a LOT cheaper than other places in Hawaii. You mention not wanting traffic -- the Big Island is pretty sparsely populated, given its size, and has a vibe not unlike Bonaire's. Also, like Bonaire, there are a couple of truly stunning beaches. Unlike Bonaire, the eastern side of the island is rainy, green, and lush, and of course you have active volcanoes which are a blast, no pun intended.
Coincidentally, I am also going to Kona in September, and found that car rental prices are MUCH cheaper through COSTCO. In fact, COSTCO is key to an affordable stay in Kona, for food, gas, and pretty much anything else you need as well. Eating out in Hawaii is extraordinarily expensive.
Hope that helps.