I hope this helps! Please don’t be discouraged by editor’s rates. Many of them do this full time or to supplement their other income with their business. The quality of service is not necessarily tied to project cost, but hiring anyone who is a contractor or freelancer often means you’re getting one-on-one personalized attention you might not get if you worked with, say, just the editor of a publisher who could see your book as a quota to fill. Just my two cents!

The single most decisive factor should be the quality of the edit itself: Will this editor help improve your book? In order to assess this, nothing beats a sample edit (even if you have to pay for it). Testimonials and credentials (such as experience at a major NY publisher) can help you narrow your list, but you should submit the same sample to a variety of editors and compare their work side by side. Some editors will push too hard, and some won’t push hard enough; some will simply “get” your writing, while others will seem to speak another language entirely. In my experience, the editor’s résumé is far less revealing than the quality of the sample edit. In fact, the higher an editor’s pedigree, the more reluctant the editor might be to provide a sample edit. Don’t be afraid to insist: no one should expect you to invest in a car without a test drive!

When you get that email, particularly if it's your first book, make sure you are well-rested and in a positive frame of mind before you open it. If it’s your first book, the editing process will be hard on your ego, but remember, the editor’s job is to make your book better and help you learn the craft. You are paying for them to give you critical feedback, not to pat you on the back and say ‘good job.'
Although many writers talk about having friends, family, and old college professors help them edit their work, that’s really not the ideal way to go about the editing process for a book or short story that you plan to publish. A professional editor with years of experience and training in your market or genre can provide valuable feedback and advice that goes far beyond simply correcting spelling errors, typos, grammatical errors and usage errors.
Next, it is possible to follow the road to traditional publication without hiring your own editor, with editing being done at the publisher’s expense. However, you have to be a very good writer and self-editor to get on that road, and what you write has to fit into a very marketable niche. You also need to be very patient and willing to weather plenty of rejection along the way. Don’t jump too quickly to the conclusion that this option is closed to you. Do your research carefully. There may be a small press that is just right for your book and that will be happy to help you make it the best it can be while paying YOU rather than making you pay them.
This is basically like the “Quick Kill” service – or proofreading on steroids, and again we’ll hack, slash, rewrite, fix, tweak and improve anything we can, but this time we won’t comment on the bigger picture, and we’ll really hone down on the little details, eliminate repetition, trim the writing, and make sure everything is as good as it can be.
In fact, Pressfield writes, “Resistance is experienced as fear; the degree of fear equates to the strength of Resistance. Therefore the more fear we feel about a specific enterprise, the more certain we can be that that enterprise is important to us and to the growth of our soul. That’s why we feel so much Resistance. If it meant nothing to us, there’d be no Resistance.”