Very reasonable priced. Wouldn't work here in the mountains but interesting.
You'd be surprised where those guys can take those crop dusters into. Really steep mountains probably not but take a look at some of the Palouse region crop dusting videos, they get down in the canyons pretty far. Makes a guy poop a little when he gets buzzed by one coming out of a draw, combine on the next ridge, up in the engine compartment servicing in the morning and you swear you could touch the tires when he goes over. Ask me how I know. Haha.
Best I remember, the last Grazon Next that I purchased a couple years ago was $95 for a 2 gallon jug. That is about $12 per quart. I can't imagine it is cheaper now. Usually use one quart per acre in early spring when weeds are small. Need a little surfactant as well. I can't figure out how that $18.20 per acre including the herbicide cost is going to work out for him.
Spraying pastures with a plane would be a risky occupation here with the irregular shapes of small pastures here and all the obstructions - trees and power lines. Not to mention the nearby crop guys that do not have "Grazon ready" beans that might take offense.
He may have a dealer license, markup doesn't get passed along like when you're on the receiving end of the product chain. The plane is usually the last option for guys around here. Sometimes we'll get behind and instead of trampling over the wheat we'll have it flown, or just flat don't have the time if other things are more pressing. I think we're in the $8-9 dollar range per acre then provide the chemical.