A few years back I did a detailed study of how much I should charge for pens. I calculated how many pens I got from a bottle of CA and a roll of sandpaper. I did time studies of how long it took me to turn each type of pen. I estimated electricity use and everything else I could think of.
After about 2 weeks of work I came out with a price that is very close to 3x material cost.
Save your self the bother and use the 3x material method.