I always charge for any time used for the job, that includes going somewhere to pick up a raised GFCI 4 square cover or an offset nipple (a couple items I may not always have on hand). By the time you get in your truck, drive to the supply house, drive to the job (dont forget your that using fuel), carry in materials and tools (hammer drill, ext. cord, etc...) install materials, test gfci, and clean up, take tools back to truck, write up bill. It just depends what you charge per hour, 175 might sound high when you just picture a recept right next to a panel, but they dont see everything you do to make it happen, I would say stick to your guns on your price...