Send a letter or email to the author of a text and ask them. If a book is self-published or printed by a smaller press, finding the editor can be tricky. The author of a book will be sure to know who edited their work though! Perform an internet search and look for an author’s website or personal information. Most author websites have a contact tab with information on where to send a letter or email.
In addition to the individual editors listed above, the Reedsy marketplace is full of vetted professional editors for every editing level and genre. They screen their editors and only allow the best of the best to be listed on their website. I'm a BIG fan of them because they have made the process easy for me to find the best book editors, book cover designers, and even writers to help me with my projects. Talk about awesome!
I say “most of your desired criteria” because it’s rare to find an editor who will meet all your criteria. For instance, you may have to pay a few hundred to a few thousand dollars more for your top pick. Or, you may find someone at your precise price point, but their experience isn’t quite what you’d like it to be. You must be the one to assess what trade-offs you’re willing to make.
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!