Ceiling Repair Consultation Needed

I'm looking for a professional consultation on a sagging drywall ceiling. The sagging is minor, and the ceiling is mostly intact. There are no visible signs of damage, such as water spots or cracks, and no apparent cause for the sagging... (Budget: $250 - $750 CAD, Jobs: AutoCAD, Building Architecture, Building Design, Building Engineering, Building Inspection, Civil Engineering, Construction, Structural Engineering)