Most NZ commercial courses cost around $2000-$2500. Some dont include the chopper flight down so you have to factor that in too.
I found the Best value courses were run by the NZAC which were around $1000 Aussie bucks (with our good exchange rate). We saw a few of them being run at the unwin hut in January, plus a few other courses run by the canterbury mountaineering club, also based at the Unwin hut. I think they're cheap because they're run by other club members.
Another mate did his at the Nehru institute of Mountaineering in the Indian Himalayas for 5000 rupees ($100 USD) for a whole month course. Foreigners pay a little more, but if you have a month free, it would be an awesome experience to be learning skills whilst totally immersed in the real mountains! It was like military training where you had to get up and go for a run each morning and clean the poo..., etc.
http://www.nimindia.net/..
I paid over $4000 for my 2 weeks in Alaska, while pretty awesome, I still dont think was worth it. I would rather spend that extra $$$ on gear or another trip.
We met up with other mates who did different courses, compared what we learnt and found we pretty much learnt the same things.
A mate did his 1 week course for $600 in Chamonix + $2000 airfares and had much better scenery than we did .
so it all comes down to what you prefer. if you have multipitch experience, as mentioned it might be better to just hire a guide with some mates and get a tailored course done up.
My first mountain climbed after the course was aspiring with a guide and its a good mountain for someone new to the game. Last month we attempted some routes with some very experienced mates but found it was totally too gnarly for me when the ice beneath my feet started breaking away.

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I would feel that Cook also would be a real challenge for someone new to the game. Its a good goal eventually but keep in mind there are many nearby climbs better than mt cook itself. Cook is mainly famous because its the highest.
here's a good read for you if you're considering cook:
http://www.chockstone.org/Forum/Forum.asp?Action=DisplayTopic&ForumID=2&MessageID=7978&Replies=8&PagePos=0&Sort=#NewPost