The cost of the work obviously will vary considerably, depending on the type of work in the assignment, its length and complexity, the turnaround time required, and your budget. I am not cheap, and urge you to beware of people who feature their bargain rates. The rate would be a little different for a student paper than it would be for a major research agency whose reports are lengthy and technical, and I have done plenty of both.
I am reasonable, however. If the project is of a significant size, I will offer you a 5 page (a little more, if it’s very large) sample of editing of your document pro bono at your request. You ought to know the quality of the work of the person you’re hiring.
I will do everything possible to work within your budget. If the preceding doesn’t indicate that I am flexible, I don’t know how to demonstrate it.