demo cost estimate - sixplex

[Nate Wright]

Doing projections for a reno.  
6 unit multifamily that we need to take back to the studs.  Ceilings need to go too, but floors are fine except for a few problem spots. 
5,000 sq ft.  6 kitchens, 6 baths, and about 35 total rooms, closets, hallways, etc.  Mostly drywall, but also lots of plaster & lathe. 
How on earth do I estimate how much this might be?  Do I get a demo guy to come quote it?  My other deals never needed this sort of demo.
My shot in the dark is $30k.  Should I be closer to 50?