Most of the tents I've seen in the NZ campsites do remind me of when I were a lass - in the 1970's . Lots of big square canvas, roped to old caravans and trailers and a definite scout camping look to them... Ditto the caravans - I think a job lot must have been brought over from Europe in the 1970s and have been doing the rounds ever since!
Prices for tents here vary. Kathmandu is one of the leading outdoors suppliers and definitely the most pricey I have seen - but they have an up to 60% off sale on at the moment - we got a good sized four man tent for $299 down from $599 (which really makes me wonder just how much profit they are making on their usual prices)... I think the six man equivalent was about $399 in the sale. These were both dome tents, and nylon flysheets. For something more substantial, canvas, you'd probably be looking at well over $1000 at the normal prices. So expensive if you are earning kiwi $$$, but if you still have GBP to spend it might seem cheap.
Doyles is another chain, cheaper than Kathmandu by a wee bit. Second hand tents are readily available both from stores like Cash Convertors and on Trade Me. Quality and price variable.
K-mart, the Warewhare and other discount places also sell tents - but we reckoned that if there's one thing you want a bit higher quality from, it's the thing that keeps you dry!
HTH