score:4
Skinny, a company which uses the Spark network (which means NZ is very well covered by them) have a $20NZD a week unlimited plan (data, voice, texts) on pay-as-you-go (but it comes with a slowdown after 10GB of usage per billing cycle), and on other plans have an option for "data binge" which is unlimited data per use, and a 12 hour data binge costs you $4.
Sims cost a few dollars at most supermarkets and general grocery retailers (often called dairies/dairy's here in NZ - spelling noted).
Top up can be done via an app, text message, automated phone call.