Estimating the Cost of Writing and Editing
http://www.webpagecontent.com/arc_archive/135/5/

McAlpine, Rachel
Quality Web Content
2004

Abstract:

The cost depends on how long and complex the document is, and how much editing is required. Most editors have a fixed hourly rate, and will quote for a job after they have studied the document. Skilled wordsmiths usually charge more per hour, because they do the job faster. When you find a fine wordsmith, handle with care. They are not exactly thick on the ground.