Short answer: Automate savings on payday. Reduce rent. Cut discretionary spending. Treat KiwiSaver as forced savings.
Pay yourself first. Set up an automatic transfer to savings on payday. Reduce rent by flatting with others or moving further out. Cut discretionary spending. Use KiwiSaver contributions as forced savings. Every dollar you save is a dollar less you need to borrow.
Income: $4,000/month after tax
Rent: $1,200/month
Automated Savings: $800/month
Kiwi Saver: $200/month
Remaining: $1,800 for bills and spending