Another vote for Island Divers. They have good variety in their daily dive schedules and don't rush you if you've still got air. The dives are still DM-guided for the most part, but they give you a fairly long leash.
Unfortunately I haven't done any Oahu shore diving, but I've been there a half dozen times and always boat-dive, on the leeward side most of the charters head out to the nearby wrecks, most of which are close to shore, in the 70-110ft range, and fairly sanitized, but still lots of fun for good-viz resort diving. The common sites by Waikiki are several barges, the YO, Sea Tiger, and San Pedro, and the single seater WWII Corsair fighter. Last time I was there, it was about $80 for a two-tank morning dive. I checked around a few other places and prices were in the $120s. The economy is pretty slow there and it seems prices always fluctuate independent of high/low season.
I've also dove with Waikiki Diving (where I got certified). On the last couple of dives there we had a DM/Instructor off solo diving, I assume he knew his way around. The crew just bid him adieu and trusted him to do his dive and find his way back to the boat (which he did). The main drawback is that they pack smaller AL tanks for the second dive, which tends to be at shallower 30ft reefs used for OW cert dives.
