Ignore the cost - players simply don't want to travel 6-12 hours return every Saturday. When you're young and ambitious it's tolerable. But as the reality sets in that you're not gonna make the All Whites, losing most of your weekend sitting in a bus ain't it.
I doubt National League teams want to sit on a bus for that long.
So for local league stuff the cost of it is bonkers. Hiring a bus for a day can be from $500 - $2500 depending*, so cheaper end would be about a grand. More or less the same if you want to rent a couple of people movers. Do that every second week and it is minimum $9k, but more likely $15k for the season just on travel.
I'd say most clubs struggle to keep the lights on at the best of times. I can't see Wainui driving to Whanganui, Taranaki or Napier every second week.
Any time I see an NZF decision my first question is, who is actually asking for this?
* and yes I absolutely did take time out of my day to google the cost of hiring a bus hahaha