We were sponsored by our son (Parent visa) and were completely puzzled as to why we were never asked how we were going to manage day to day - it was all loaded on him, what his salary was, checking where he worked, can he offer us a roof over our head - then he signed this document infront of a JP in NZ. Bit scary for him!!!
We will be self sufficent when we arrive in NZ but the onus was on our sponsor not us. The only other way I think would be to bring in lots of money and lock it away for a number of years - or of course, open a business and employ lots of people.