Azza has pretty much covered it.
The cabins at the Tutukaka campground are reasonably priced and very convenient for an apres-dive beer at the Schnapper Rock bar in Tuts.
The motel at Ngunguru is a bit more pricey, but you at least get showers and toilets in the suites as opposed to having to walk over the campground to get to them.... bedding is included, whereas it's bring a sleeping bag at the campground.
The sports bar in Ngunguru is a good place to get a beer and the chef there is excellent. Alternatively, the fish and chip shop makes the best mussel fritters in the world. The cafe, Solaris, opens early and does a good breakfast - and customer service is better than at Schnapper Rock.
Dive! Tutukaka (
www.diving.co.nz) are definitely the best charter for the visiting diver - they won the PADI Asia Pacific dive operator of the year, they really do look after you well. The diving is fantastic, but depending on what you're used to it might be an idea to take a guided dive (free of charge) on your first dive so you can get an idea of what to look out for.
I'm unfortunately teaching that weekend, otherwise I'd offer to give you a lift up from Auckland and go for a dive...