I just looked at this thread and am I right that the total square footage is about 787 and the price is about $74/sq ft?
You're not thinking 3D. The ceiling is around 500 sq. ft. by itself. Add the walls, stairs, hallway, etc. and I bet it's more like 2,000 sq. ft. worth of drywall. That puts it around $1.50/sq. ft. which is about average.