phrases - Is "the human cost of inaction is inefficient and even deadly" proper english

This is taken from "Streetfight: Handbook for an Urban Revolution":

The human cost of inaction is inefficient and even deadly, but the political stakes for people who design and build city streets couldn't be lower.

I know that there is a phrase "deadly cost" but what I wonder is whether it is proper (or good writing style) to break phrase like that and say "cost is deadly". Second point, is I am not sure if it is proper English to write "cost is inefficient".