The cost is up to you. Enago operates globally with regional teams supporting researchers locally. You can read more about the process of how to find an editor here. So how much are you willing to pay to make sure your book or paper is polished professionally?
Dissertation editing services are usually priced per the number of words in the manuscript.
We can use Google Docs, too, although the version control is inferior to working with a single doc file. Create your free account and start exploring your options with Wordy today.
You will see a broader range of prices here, and these figures are usually commensurate with experience.