This can be a very difficult number to figure out. Some journal editors get paid, some don't. Some publishers have staff for the review process in their own offices.
Some editorial offices have a person to handle the peer review AND the copyediting of the material.
But, again, this varies dramatically based on the complexity of the content. If you mean the work the journal editor does to edit the content, that would be in the figure above. I suggest contacting Don King and Carol Tenopir at University of Kentucky. They have done quite a bit of analysis of journal costs.