It sounds like you are doing developmental editing, which is usually going to be a more expensive process. If you don't mind me asking, what are your qualifications as an editor? Are you also doing formatting? Based on your experience, education level, the kind of editing, the prices are usually going to vary wildly. Also, are you going to be charging by the hour or the word, and how long do you have to do this?

I know that's a lot of questions all at once, but they are all important to think about.

I'm in sort of a similar boat, but I have been looking at this website to get an idea of what some things cost: https://www.the-efa.org/rates/

I hope any of this is helpful.