I have the Canon 10-22 but would agree that the Sigma 10-20 is a good alternative for less money. However, these ultra-wide zooms aren't a substitute for a general purpose lens like a 17-50 or whatever, and you'll find it difficult to get both for your budget.
Which way are you flying to NZ? I've gone via Changi (Singapore) a couple of times, and there may be the opportunity to buy there and save quite a bit on UK prices. There are photo stores in the airport. Don't buy in NZ - generally more expensive than here.
