I usually calculate the cost of a project by the number of words submitted, with fixed rates for proofreading and copy-editing, calculated per 1,000 words. Generally speaking, using word rates means the price for your project can be calculated from the start, ensuring no nasty surprises at the end. I require 50 percent payment up front, with the rest due on completion. However, if the text is to be submitted in various portions, then each portion can be priced individually. This is useful for authors who are still working on some sections of their project.
I charge different rates for proofreading and copy-editing, calculated per 1,000 words. Since I am based in Britain, the prices are calculated in British pounds (GBP).
Proofreading – 13 GBP per 1,000 words
Light Editing – 18 GBP per 1,000 words
Copy-editing – 22 GBP per 1,000 words
Heavy Editing – 26 GBP per 1,000 words
Additional editorial services, such as writing book blurbs and synopses, may be priced on an ad hoc basis.
Tell me what you need and I'll give you a free quote.