A few things to think about when trenching:
2.soil climate? sand,clay
3.what are you installing? sprinks
4.roots and rocks?
5.machine V hand digging? I prefer a machine
6.Heat/Humidity as already stated? digging in the sun all day is not that much fun
we charge 1.50 a foot with the 255 to install 1 inch NSF poly 8 inches in the ground.