Here's how I do it, comment/suggest changes

I charge the customer for all the materials (no markup)

I then charge $15 per hour.

a civic (approx 3 hrs work) (3*$15=$45) plus $10-$15 materials = $55-$60


I work in their driveway, and only need water and electricity.
I am a one man team, and don't pay for health insurance ETC.

thanks,
nick