I have a house to make a estimate on that has 1400sqft of paintable wall surface and approx 80ft of trim. The house needs to be power washed, cleaned with TSP, silicon and some putty repair, scraped/sanded. 1 coat of alkyd primer, 2 coats of premium latex paint. Trim will be a different color than the house with the same prep involved. The house paint is in bad shape and needs lots of prep before the finish paint. Not sure how much to charge for this kind of exterior work?
Time and material is the best way to bid almost any paint job. Consider how many hours/days of labor times the preferred wage now add all materials that will be needed, include gas, then add a small profit percentage for your company to cover taxes/insurance/etc, 10-15% should cover it.
Added prep work always takes longer and costs more. Make sure to give a comprehensive proposal with all steps and products used written down. Then explain all of this to the customer. If you can think of options that could reduce or increase the cost but add value include these as priced options.