This all depends on where you want to ski as all the resorts have their own price range. It also depends on the type of pass you want.
If you plan to ski at one of the Wanaka’s winter resorts, Cardrona (suitable for beginners), Treble Cone (suitable for advanced), Snow Farm or Snow Park NZ, then an Adult day pass will cost you between $75 to $99 dollars. You can also hire equipment from the ski fields from a full ski hire to just gloves which makes it very convenient.
You’ll also find that the ski fields provide Lesson Packages including lift, lessons and hire equipment which work out a better deal at around $80 depending on whether you want a beginner or intermediate package.
With regards to booking you can book on the day you arrive at the booking office at the mountain or online.
No1guide has written an article comparing all 23 Ski Resorts in New Zealand to help New Zealanders and Tourists in finding the best ski resort for them. View a comparison of the New Zealand ski areas where you can find a list of prices and hire equipment details etc.