I charge per hour or if they want a quote then a lump sum based on an hourly rate for my time. It sounds easy but what is your time really worth. You have to calculate your "wage" but business expenditures. For me to make the number I want that turns out to be $125/hr for standard photogrammetry flight but I also have separate rates for mobilization, lidar and tech (CAD, modeling & analysis) just as if I had employees that I would pay different rates. Then I can itemize on a quote when needed. Itemizing always makes the clients more comfortable because it gives them a glimpse to what is actually going on rather than just flying a toy...