There are a number of companies in New Zealand that run terrific, budget friendly services around the country. Travelling New Zealand by bus is budget friendly and still affords you plenty of flexibility. InterCity, Naked Bus and Mana run frequent services between most towns and cities in New Zealand. Some journeys are long but if you are willing to put up with these longer bus rides, there aren’t many places that you can’t get to with one or a combination of these bus companies.
If you’re considering this option, Bunk recommends buying one of the backpacker passes. These will give you a certain number of journeys around New Zealand and will often include a ferry crossing to each island.