We typically work on a "Time & Materials" basis, charging for hours worked (which sometimes includes travel time, and time to acquire & deliver materials), plus the materials costs. This is true especially for smaller projects, though we provide a free educated "guesstimates" (formally know as an "estimate") calculating the expected costs. For larger projects we will often work on a "fixed price" basis, or "time & materials" with a "not-to-exceed" price cap.