I edit a wide variety of texts, including website content, advertisements, reports, speeches, film scripts, academic theses, and articles for publication in newspapers and magazines.
With many clients my role is that of a copy-editor, which means I not only correct the errors in a text but also ensure its style is appropriate for the context, and potentially do some rewriting. But for other clients I do proofreading, which usually means just checking through a text for the last time before it is published, without making any significant changes.
Please see References for comments from a few of my clients.
Rather than basing my editing fees on the quantity of words or pages, I believe it's fairer for the client if I charge according to the amount of time I spend on a text.
The advantage of a time-based system is that the price the client pays depends not only on the length of a text but also on its quality when I receive it. That means a long text that needs only a few changes might be edited more quickly, and therefore more cheaply, than a shorter one requiring numerous alterations.
I generally offer a free quotation based on the maximum amount of time I think the editing will take. My final price is sometimes slightly below the quotation, and never exceeds it.
But if you prefer to know exactly how much the editing work will cost, I can of course agree a fixed price in advance.
If you don't need your text to be rigorously edited - for example if you're not concerned about issues of style - I can of course limit myself to correcting any grammatical or spelling mistakes.
If you don't actually have a completed text but only the idea for one, or perhaps just a few preparatory notes, I'd be pleased to discuss the possibility of doing all the writing for you.