Or just plain elimination of spelling mistakes?
The phrase I use in my marketing "With your peace of mind in mind!" is not just a phrase, I live it. My aim is that through working with me you have peace of mind, you can rest and be assured that I do my absolute best to retain YOUR unique voice, YOUR writing style, and at the same time eliminate anything that doesn't work for your reader. Check out the differences between copy-editing and proofreading to get clear about what you would need.
To give you a rough idea about how long different workings on your project take, what is usually included, you can check out this page. But please bear in mind, because every project is unique, there is no solution or rule to fit them all! I'm sure you appreciate this :)