Estimate time need for repair, multiply that by what you charge per hour. Add materials, or estimate materials by charging 2/3 of your hourly rate x the amount of hours for the repair/paint. For example your Volvo hood, say you estimate 3 hours to strip and re-prime, say there are a few dings, you estimate 1 hour, then you would have to estimate paint time, this is where estimating software comes in handy, but a rule of thumb I use is $175 per panel (this includes budget materials like PPG Omni base, Transtar clear) $75 per blend panel.
Nothing is hard and fast it is simply a best guess, estimating software helps, as does experience. There is no one answer to your question. Try to estimate the amount of hours the total job will take you. Then figure how much materials you think you will use. Multiply your hours by the rate you want to charge then add in materials (customary to add 25% to the cost of materials). That will give you a number you can tell the customer.