A good editor is invaluable when starting out. Later on it perhaps depends on how complex the story or writing is. Editors can be looking for similarity not originality. The final script a poor representation of the original story or article. An article of mine, which was picked up by Wikipedia for its originality and informative ideas was given forty edits from around the world! It was like a mechanical invention rather than an interesting article in the end!

I cannot speak for all editors, of course, but I know I and many of us would be open to editing just part of your book at first, say, a particular chapter or two that you sense needs a lot of work. That is often enough to show you mechanical errors that you tend to make repeatedly. You can then go through the entire manuscript yourself looking for as many of the same kind of errors as possible. You will sharpen your basic writing skills in the process, and it will pay off in all future projects.
Start at the top of the copyright page and work your way down. Copyright pages can be formatted differently, but they usually start with the publisher, date, and location of publication. Slowly scan each line to look for an editor’s line listing. The editor (or group of editors) are usually listed in the middle, underneath the publisher’s information, but above the country and printing number.[3]
Hiring a grant writer can give you a competitive edge when applying for financial grants for your business or nonprofit organization, or as an individual. The cost to hire a grant writer can vary depending on their academic background, areas of expertise, previous grant writing success and years of experience. According to the Grant Professionals Association, grant writers should be paid hourly or by flat fee. It is unethical for a grant writer to accept a commission or percentage compensation of grant monies received. They can, however, be awarded bonuses in line with the hiring company’s prevailing practices. Here are some examples of average grant writing fees:

“My books have very complicated formatting with over 100 illustrations each, external links, and numerous bulleted lists. None of the formatters I contacted would even take these on but John said “No problem!” He completed my original three e-books quickly, for a more than fair price, and they look great. I have no hesitation recommending Ebook Launch’s work to other e-book authors!”
I’d add that for UK writers, the Society for Editors and Proofreaders (SfEP) Directory is the best place to search for editorial professionals. Each editor has been vetted for professional competence through the Society (you have to be assessed to become a Professional Member or Advanced Professional Member), so it’s a pretty trustworthy source: http://www.sfep.org.uk/directory/directory.asp
Start with a google search and see what comes up. Click on a handful of options and see if you can find an editor who is specialized or who has edited books similar to your own. An easy way to do this is to open just a few of your favorites in tabs and check out each editors’ website and about me section. Take a look at their testimonials. See if any stand out to you.
I just published my fourth ebook novel recently and I've used Ebook Launch every time with very satisfactory results. They always promptly turn around the cover and manuscript formatting - and as an added bonus, they always promptly and happily answer even the stupidest questions I come up with. Adrian is very easy to work with and Dane has repeatedly come up with cover ideas when I was fairly sure that it couldn't be done.
The greatest benefit of an editor is that he or she is not the author. An editor is someone else. Some editors are professional writers, but every single one of them is a professional reader. As a writer, you’re probably a voracious reader, but you can never be a true reader for your book. By bringing forth a book into the world, you’re asking other people to read something you’ve never read. If you sincerely want the book to be the very best that it can be, then you must ask someone else to read it first. You owe it to your book, to yourself, and to your readers.
I keep second guessing myself on things like where a space should go when someone is talking and if I have to keep saying “He said” “She said” etc., over and over. Or Mom vs mom. It goes on and on so I am thrilled to read Trish’s response about hiring an editor for a chapter or two. I would love to do that when I finish before I do a complete rewrite myself. I think that would help save so much time.