I'm sure someone with an aircraft colour scheme/design background will come with more specific information, but I wouldn't think the cost would be substantially more than a normal paint job. Granted, you have the design cost and (maybe?) extra costs for unusual colours etc, but I'd guess the cost of getting it put on would be similar to the normal paint job.
Of course, if they plan on repainting it back in std ANZ colours once the RWC is over they will have to pay for that too. Here's hoping they don't repaint it, I quite like the colour scheme - looks better than the green 737. Is that one still flying in those colours? I haven't been around to see it for a while...