When is a building a lost cause? Rehab cost too high?

[Janelle Hicks]

At what point is a property too far gone to rehab? 
I found an 9 Plex, fixed up it could be worth about 400k based on income valuation. But it needs EVERYTHING. Place is a dumpy/disgusting, been vandalized, no floors, bad roof/ birds got in, kitchens barely exist, full bathroom reno,  needs all new plumbing and electric, new roof, new windows, all appliances, obviously paint / fixtures/ doors etc. Only thing it really has going for it is sturdy plaster/ structural integrity. Honestly I'm sort of surprised it hasn't been torn down ( except that's gotta be expensive as hell). How do you figure a rehab cost for that?  I figured easily over 100k just to make it habitable...but how much over? How do you determine if a building is Worth saving?