Cost of production plant I'm struggling to find a macroeconomic index which embodies the cost to run an average production plan. 

My problem is that I wanted to divide the annual average cost per employee (which I already found to be gross income per capita) with the cost of running an average asset (e.g rent, energy and other expenses). 

Did such an index exists?
If you are looking for data on costs for production plants you might consider the BLS productivity data https://www.bls.gov/mfp/mprdload.htm.

Under the combined sector and industry multifactor productivity excel file you can find cost measures organized by NAICS (North American Industry Classification System) at the three digit level [https://www.census.gov/cgi-bin/sssd/naics/naicsrch?chart=2012] .    

Depending on what type of production plant you are looking for there is data by energy usage, rent, and other types of costs.