orders in council are still subject to judicial review

I'm going to pretend momentarily that I understand constitution law.

Yeah, there's probably a need to distinguish between a judicial review of an administrative decision and a review of an Order in Council that concludes it is ultra vires (and therefore invalid).

Often judicial review considers an administrative decision (in this case, the recommendation of the Minister to the Governor-General) to examine whether the decision-maker followed the right procedures and properly considered all the factors they were supposed to consider in making that decision. If it turns out he or she didn't do so, the court asks the decision-maker to reconsider the decision. In the case of the law in question, a review of the recommendation is not possible due to 6(3).

In saying that, I'd assume that despite 6(3) the Order in Council itself could be declared ultra vires (and therefore invalid) if it tried to do something that primary legislation doesn't allow it to do.

So if that's right, you could challenge whether the conditions in 6(1) were met (the Order in Council was "reasonably necessary or expedient for the purpose of this Act") and you could also challenge the Order in Council if it did anything that 6(6) says it can't (e.g. it can't modify a requirement of the Bill of Rights Act). You just couldn't challenge the procedure and considerations required to make the recommendation under 6(2) (i.e. taking into account the purpose of the Act and consulting the recovery commission).

However, read as a whole the Act does not intend to make Gerry Brownlee into Parliament. Which is why the bit about existing provisions is important, since the overall import of the Act is to allow him to relax existing statutory limitations to assist with the reconstruction. Even a National government is leery about giving over its legislative powers to someone who's not Parliament.

I agree that relaxing existing statutory limitations was certainly one of Parliament's intentions. In particular, section 3 (the purpose of the Act) says that part of its purpose is to:

(c) enable the relaxation or suspension of provisions in enactments that—
(i) may divert resources away from the effort to—
(A) efficiently respond to the damage caused by the Canterbury earthquake:
(B) minimise further damage; or
(ii) may not be reasonably capable of being complied with, or complied with fully, owing to the circumstances resulting from the Canterbury earthquake:

Its purpose does include more general components, such as:

(a) facilitate the response to the Canterbury earthquake:
(b) provide adequate statutory power to assist with the response to the Canterbury earthquake:

My understanding is that a court's view of the overall intent of an Act helps it to interpret the Act's specific provisions. (And purpose statements help courts by telling them what Parliament's intent was.) This is particularly important if a provision in an Act is unclear, or seems to conflict with another provision in the Act. However, even if an Act is understood as being primarily intended to do a particular thing, that doesn't override its specific provisions, and doesn't prevent its specific provisions from being misused by the Government or anyone else. (That is how the concept of "loopholes" comes about.)

I find it hard to see that, even under the most conservative reading, this Act couldn't be used to create provisions that go beyond mere relaxation or extension of existing statutory provisions. 6(1) is very general:

The Governor-General may from time to time, by Order in Council made on the recommendation of the relevant Minister, make any provision reasonably necessary or expedient for the purpose of this Act.

And there is even 6(3):

The recommendation of the relevant Minister may not be challenged, reviewed, quashed, or called into question in any court.

S6(4) says "an exemption from, or modify, or extend any provision of any enactment".
That's what limits his power. Yes he can extend or modify provisions, but the provisions must already exist. He cannot create new provisions

IANAL, but 6(4) is an example of what the power in 6(1) "may" do. And 6(7) is quite explicit: "subsections (4) and (5) do not limit subsection (1)."

His reach is limited to what can be done under existing legislation, he cannot invent entirely new powers.

How do you reach that conclusion?

On a more practical level, and ignoring whether or not it is a good idea, could Gerry Brownlee step in and set region wide prices for items such as petrol and milk under the wide ranging powers he has?

If it were a reasonably necessary or expedient step to assist with the response to the earthquake, then yes: http://www.legislation.govt.nz/act/public/2010/0114/latest/whole.html#DLM3233036

There's a couple of things I don't understand, and they might be stupid things, but hey, I'm not proud.

If the idea is that prices are the most efficient way of finding out who really needs the stuff; and if you need a govt subsidised work around to make sure that the people who really really need the stuff can afford it, then the idea is a bit broken. No?

Where does the govt get this info about who to subsidise? If that is info the govt already has, then what info is gained from the pricing business?

Secondly, (and it's probably already been talked about but I just don't recognise the language being used), if someone has a large supply of money, then each dollar isn't worth as much to them as someone who has a small supply of money.

Well, quite. Translating them back into economics-speak, those are two of the most important criticisms of Kaldor–Hicks efficiency as a welfare criterion: (1) The absence of suitable mechanisms and information to compensate the losers in "efficient" outcomes, and (2) The diminishing marginal utility of wealth. (Nevertheless, price signals are still a pretty good way to find out who really needs stuff.)

I too am confused about what this argument is about. The recommended $4 per litre pricing of petrol has apparently not been implemented. If the residents of the South Island are rational agents and have freely chosen not to sell at such prices, doesn't it follow that such prices are irrational?