The refs say that FIFA pays for 40 flights from New Zealand. There is a good chance this is just a cash grant equivalent to the cost of 40 flights. Given we have a number of players in Europe, we'd reap some savings in that regard. And that could end up paying for a couple of extras. Although accommodation and other flights between warm up games aren't covered so there would be quite a cost there that would NZF needs to cover.
Regardless 21 hanger ons seems like a lot, and as CT says, doesn't really seem like good value for money.
And recall that NZF took a lawyer and their CEO to a one off game in NCL. So for a organisation that often claims to have no money, from the outside there doesn't seem to be much consideration placed on value for money spending.