After converting NZ$ to US$ and KG to LB the cost of the 18% non-organic is pretty close to what it is here.
The percent protein in the feed is not the critical thing, it’s how much total protein they eat in a day. That comes from everything they eat, not just their feed. How many grams of protein they need each day will depend on their size, whether they are laying, things like that. A hen laying an egg will need more protein than a rooster, even if the rooster is a lot bigger and needs to maintain his bigger body. A hen molting needs more protein than a hen not molting unless she is laying eggs. That’s why they quit laying when they molt, to use that protein for feather growth instead of eggs.
The commercial hybrid laying hens are fed a feed of about 16% protein. They do not forage and they do not get any treats. The feed is all they eat and it works for them. Since yours forage and they get treats then their feed constitutes only a part of what protein they eat.
It probably varies a bit with the individual crop but barley has about 12.7% crude protein, wheat about 15.9%. If you feed much barley you probably need to feed a higher percentage protein feed. With wheat not so much.
Since yours forage you can’t tell how much total protein they are getting each day. That’s going to depend a lot on the quality of your forage. If your forage is a manicured yard with nothing but immature grass, there is not a lot of forage value in it. If you have a farm where there is a variety of grasses and weeds, grass and weed seeds, various creepy crawlies, rotting vegetation for them to scratch and feast in, and maybe some cows or horses where they can scratch in the poop and get lots of concentrated nutrients they can do really well. In those circumstances they can pretty much feed themselves and do really well, but in winter you do need to supplement when the quality of the forage goes down.
They can surprise you at how much forage they can find even on frozen ground and I don’t know the quality of your forage, but I’d consider that 18% feed to be plenty adequate. I think you are good to go with it.