Please help me understand the idea of charging for four edits. Are you working on bodies of written material? and charging per error corrected?
As an editor myself, I am wondering how this could work because so many suggested changes are discretionary in nature and some number of others are just plain wrong. And is a change actually a deletion and insertion (two charges)? Is the removal of a comma equal in worth to the rewriting of a sentence? Some solutions require a mere keystroke, and others are real head-scratchers. And all that assumes that you know what the client meant to say, which can be hard to determine from error-ridden text. What do you charge for an intelligent and well-written query without a change?
Besides, if you are working on something that’s in very good shape, you could spend a lot of time going over pages that don’t need any changes, but the absence of changes represents an investment of time and many editorial decisions. Getting paid nothing for that would not be fair compensation for the effort put in.
Customarily, rates are based on either unit of time or unit of text (such as a page or a number of words).
If I were your customer, I would want to see very clear definitions of what I was paying for before I engaged your services. In fact, having been a party to many futile exercises over the years in which defining and quantifying editorial changes was the aim, I would love to see them in any case.