"How much will the editing cost for my book?"
What a reasonable question to ask. What a difficult question to answer!
It's much like asking, "How long is a piece of string?"
Editing costs are related to the time the editor spends on the job. Here are some factors that draw on the editor's time:
Check out the FAQ page for types of editing.
Some editors give a flat fee. So much money per word, regardless of how difficult it is to edit. I don't.
Every piece of work is unique and needs its own unique response from the editor.
No one works for free.
What do you suppose the one-price editor does when his clock for your project runs out?
There is a better way...
I offer a sample edit of 500 words. The client receives a detailed response to his or her writing. I include a quote for the various services I offer. (Sometimes writers send longer sections so I can get a picture of the overall structure. I skim the longer piece, but I can't afford the time to do sample detailed edits on more than 500 words. I love editing, but I do have to eat, too.)
The good news is that when you get your sample edit, you know exactly how much your editing will cost. Even if your writing turns out to be much more difficult to edit than I expect, you pay only what I quoted.
Note that I originally wrote this page in 2003. Writers who waited years to hire me after sending the sample edit had their quotes honoured even though 2008 had happened in the meantime, standing my financial situation on its head. I now put a time limit on my quotes, but I still stand by any quote made before I began putting in a time limit. And if I think it's fair, I honour quotes that have gone past the time limit.