the box of that dumptruck would literaly have to be filled to the brim to hold 20 tons, typical 12 yard dump box hauls 15 tons to be road legal and thats with a tag axle, that truck with no tag would probably only haul 12-13 tons legally on MT highways.
not sure what spec material is #57, I have heard of type 51 engineered gravle with vegetable oil mixed in to help with dust and compaction.
locall a ton of 1 1/2 minus is going for $16 bucks a ton if I haul it myself, If I have it trucked in it costs me $450 for 15 tons delivered, so $30 a ton delivered 7 miles from the pit.
we dont have much granite around here its all shale, so the type of rock might be a factor in price.