The local libraries have books and tapes etc you can borrow. Only thing is you can't hire them for too long. You can buy them from bookstores like Borders, but they're usually about $100.
Have you learnt a language before? You could learn one through the correspondence school of NZ. I did a correspondence course through them and it was really great, they send you all the material as you need it, you can call them up for help, and it's nzqa. Adult students over 20 pay $100 a course... Heres a link if you're interested
correspondence school nz, it's just a list of the courses you can study.