Hate it when we start thinking we can quote on this site. Too many variables not the least of which is we live in divergent parts of the country most of the time.
In this case, contractor is providing all materials? 5/8", 1/2" etc. Corners treated how? Quality of the primer? Any tricky angles or shapes to work around? How many openings for lights, outlets, switches? When does it need to be done and how soon is the site available for drywalling? 800sf off the floorplan or that is the surface area of ceilings and walls needing drywall? Etc., etc. etc.