hello
moved to Christchurch from London a year ago, but my parents are Kiwis and moved back here in Dec, so it's slightly different for us (and I am a citizen)
anyway
Cost of living: it's not actually that cheap, certainly not as cheap as it used to be. That's especially true of Auckland and Wellington. Books/CDs/DVDs etc. particularly expensive. When you compare prices of things to sterling, yes many things are very cheap BUT once you're earning in NZ dollars they're not.
HOusing: if you bring over a lump sum from the sale of a UK property, you will probably be able to buy something lovely. We have a 3 bedroom house mortgage free from the sale of our cruddy 2 bedroom flat on a dual carriageway. But average price of house v average salary is as scary a multiple as it is in the UK. Auckland/Wellington house prices are much, much more than ChCh, Dunedin is cheaper still. However salaries are also significantly higher in Auck/Well than they are down here in the South Island.
Most older style houses are one storey, they often have lots of outbuildings/garages/sleepouts and decent land etc. be warned they tend not to have central heating, proper insulation, double glazing etc. so it can be cold; our electriciy bills over the winter have been terrifying; heating is heat pumps/oil column heaters plugged into the wall etc. There are plenty of more modern house too. one thing you'll get used to is there are few brick houses - very noticeable when you come from the UK.
Education: unknown here as children are 2 and 6 months, however DD attends an excellent early learning centre and once she turns 3 the government pay for 20 hours per week early childhood education. Primary schools near me are excellent. There's been a hoohaa over the main secondary qualification, the NCEA, not sure where that's all at at the moment. Some private schools offer the international baccalaureate instead.
Lifestyle: relaxed, outdoors, friendly, laid back, very VERY child friendly, feels safe, lots to do.
looking at your location options they really are quite different. Auckland is the big centre, the money making place, the place most like a city anywhere. Napier is smaller, don't know much about it apart from the fact it was rebuilt in Art Deco style after it got damaged by a volcano. Dunedin is a lot more remote - the city is quite bustly, the university means it's youthful and packed with students, it has more than a bit a feel of Scotland to it. It's a lot more remote though, and a LOT colder than Auckland! on the other hand, the South Island is STUNNING and you wouldn't be far from stacks of amazing places. I love Dunedin actually.
ACceptance by Kiwis: not a problem. Very friendly, very welcoming, and very used to poms moving over! the only thing here was DH had a small problem getting work here in ChCh - wasn't getting interviews - but a bit of persistance cracked it. Also he has no particular career; if he'd been an IT person e.g. they'd have bitten his hand off.
I could ramble on too! have you looked at the other threads in this topic; I know I've posted similar advice/ramblings before?