Set a price for the job. Find out what he wants and tell him how much YOU want for doing it. Pricing by the hour is tricky at best, even for regular doemstic work. You dont want to be charging an hourly rate for jobs like this.
And remember. its YOU who agrees the price, the client says yes or no. If they accept the price and you underquoted, then you've no one to blame but yourself. If you keep that in mind you'll not feel half as resentful as you might otherwise do.