It is very difficult to provide a concrete price structure for proofreading and editing services as there are just too many variables! In general I base my prices on the hourly rates recommended by the Society for Editors and Proofreaders (SfEP), of which I am a member. Before commencing any work I will always ensure we have agreed on a rate and approximate time frame and addressed any issues which may cause either to vary. Alternatively, I can provide a fixed-price quote for most work if provided with a copy of the document and relevant information such as intended audience and urgency. For new clients in particular, the easiest approach is to send me a reasonable sample of the document and I will get back to you with an indication of what is needed and the cost.
-Heather