My quick back of the envelope estimate is 2-3 gallons for the walls and 1 for the ceiling (2 coats on each), based upon self painting many houses. Maybe 50-60$ a gallon - that's at least $200 in paint alone. Throw in another $100 for other stuff (caulk, spackle, tape, etc), transportation, etc. Meaning maybe $650 for labor. At 50$ per hour, that's maybe 13 hours. If the cost includes all the prep work (patching, sanding, sealing, etc.), all supplies, working with windows and doors, and all labor, that's seems like a pretty reasonable estimate.