The cabins (atleast in the off season) were nice and cheap at the Karamea campground, Around 75% cheaper then Kaikoura. Because the cabins were so reasonable I decided to book one instead of pitching my tent. The campground has excellent access to the lagoons and you can get to the river mouth at low tide by crossing the lagoon. I was there during the Autumn so not many holiday makers around and the peak of the fishing was during the summer months.
There is also DOC camping at the start of the Hephy track, Something like $5 a night for a tent site.
The free caves in the National Park are worth a look, the guided cave tour was not worth the price. Just lacked the since of adventure and exploration for me.
I want to go back to Karamea, but it is not at the top of my list. If I had the whole of summer off work I would end up there sooner or later.