Have you looked at the Spark , 2Degrees and VodafoneNZ sites? I can see many options

Coverage is about the same overall for all carriers so just go for one that works in with budget 

Google is easy ' <carrier name> Data sharing

2degrees has great data sharing options with a main number on Prepaid and Postpaid

https://www.2degreesmobile.co.nz/help-and-support/mobile/products-and-services/shared-data/

John

Why not just use Skinny anyway and just bundle the amount of data you want?  Just because calling / sms is included doesn't mean you have to use it. 

Oh and no such thing as ' iPad ' plans anymore it's just mobile broadband does not matter what the SIM is in it's still just data

John

www.warehousemobile.co.nz have pretty good pricing for data only.

$4 = 500mb

$8 = 1.25gb

$30 = 5gb

Runs on 2d network so you'd need to make sure that the coverage is OK for you.  You can manage it from the warehouse mobile app