It might be arguable that the pay should be as proposed.  But it is a political killer.

Ask yourself:  Who will run for this?  People who are qualified?  People who are well known?  People who have an axe to grind?

Did you require this auditor to have a certain accounting background in education and experience?  If not, that is a total deal killer.

I don't expect that a city internal auditor (working under the City Manager within the Finance staff) would make as much as his/her department head.  Nevertheless, I would expect every department head - even the City Manager - to fully cooperate that auditor.  

The added pay is not needed.