Editing is a general term. Copy editing is a specific type. Geared towards format and grammar.
A lot of it is about the relationship you have with your editor not just the cost. Like anything research.
Some charged by the word some by the page of some by the hour but there are standard rates. If you look enough you can see the going rate.
Grammar and format.
Developmental, line and copy
If you search on enough gig sites or different company websites you can see what their standard rate is but you can find anything and everything in between.
Depends on following and experience.
Depends on who's reading it. But not long.
In the beginning most people charge per word