A Bachelor of Science might cost $20,000 NZD ($13,000 USD), extra fees are pretty low, textbooks are not cheap but professors usually try to avoid you having to buy them. In your first year you might get away without having to buy a textbook (in the maths departments at least). A Bachelor of Arts would could a few thousand less.

Fully catered accommodation is expensive. Higher end would be $14,000 NZD ($9,200) for a year. Not many students continue in halls of residence past the first year. Staying in a shared flat would cost a LOT less.

A lot of students also live with parents and commute.

The Student Loan is interest free and covers course costs as well as a portion of living costs. Domestic students also can get a Student Allowance of about $220 NZD/week (or more depending on circumstances). The allowance is welfare, not a loan.

Walking away with a degree and $30,000 - $40,000 NZD ($20,000 USD - $26,000 USD) interest free debt is reasonable. Some people will be more, others will be less because they worked part time while studying.

Repayments are taken out of your paycheck (12% of income over $19,670 NZD, so probably 8-11% of total grad compensation per year). There is no incentive to repay it faster due to the lack of interest. Most students I think would have it paid back in 11 years or less. If you learn less than $19,670, you don't have to make any payments.

The catch is you pay 4% interest if you go work overseas. Salaries are higher overseas so you will still win.

There is little to no incentive to declare bankruptcy. I have never even heard of it discussed.