Not sure about heli hire in NZ.
From what I saw most operations are for either grabbing tourists and ferrying them about showing them the sites or sling work.
I also know if hiring fixed wing on South Island (e.g Queenstown) they will not let you go wandering arund the mountains on your own, unless you have lots of experience both of mountain flying and the area.
They will give you instructor to babysit you. Same applies to the farm based touring operation.
Trust me those mountains are big and the valleys are deep, so it's not somewhere you want to get lost in low cloud. You need to know your valleys and escape routes. Also having an idea of the local weather is important, the pass into Milford closed right behind us and if you don't know where you are going it can be embarassing. Ok you might say a lot easier in helicopter but helicopter meeting mountainside is not good either.