It's free but so impressive in ended up donating $20 NZ. It's worth it and has plenty of great exhibitions from the Maori origins of NZ to special exhibits like Gallipoli WWI history. Place is huge so I'd focus on 2-3 exhibits / floors of interest and then maybe spend a couple of hours taking it all in. Easily reachable by foot if you stay downtown and nice walk along the waterfront to get to and from there.