It would be interesting to know the size of the flats in question? If its a relatively small block, that quote could be for the whole thing - not just the hallway. It doesn`t make sense to do a report on a hallway, without the rest of the building being assessed.
And, totally aside from that, sorely it is the owner / landlord`s responsibility; not the tenants? Or do you all own the individual flats, and share responsibility for the communal areas.
Personally, I wouldn`t just look at a hallway m8. IMHO, unless you`ve assessed the building, as a whole, no valid assessment can be performed.