Nothing bugs me more than a misspelled word or a misplaced comma in a book (bad or implausible plots are a close second). The mass paperback publishers generally don’t have any errors, and if they do, they are not egregious.
By contrast, self-publishers seem to skip this part, settling to do it themselves or to have an old English teacher do it (nothing personal against English teachers; I used to be one and ask advice from several from time to time). Doing your own editing is like self-diagnosing an illness. Some of the times, you’ll be spot on, while on others, you could not have been more wrong. After all, if you could self-diagnose yourself (self-edit) adequately 100% of the time, there would be no doctors (professional editors).
When I shop, I can go no frills on a lot of things if I want. For ketchup (tastes funny) and bleach (less potent), I will always pay full price. Take the same attitude with editing. It will leave a different taste in your audience’s mouth and carry less potency as a product if you don’t. Your product is part of your brand, and your brand is part of your name. Would you want the word association with your name as an author to be “cheap” and “unprofessional”?
When looking for an editor, you want somebody who has 1.) work you can check as a reference, 2.) a reasonable price. For regular copyediting, expect to pay no more than .01 per word. For example, the word count for my novel The Lost Testament was about 80,000 words. If I only needed basic copyediting (grammar, spelling, etc.), then I shouldn’t have paid more than $800. For line editing (line-by-line scrutiny), I believe you should not pay more than .015 to .02 cents per word, and for content editing (if I needed to make sure my period details for 1962 were accurate, in addition to the line editing, etc.), then I should pay no more than $3,520 for editing. I do all my own research and fact-checking, so I never use content editing. I stick to line-by-line, because the English language punctuation, grammar and syntax rules are fluid. Sometimes, you can bend them. Sometimes, you can break them. But consistency is key.
I would like to recommend my editor, Steven Manchester. His rate for line-by-line editing is $3 per page. Using the example of my book, at 80,000 words, or 266 pages, his charge would be $798 for a job that’s $2,720 to $3,520 by current industry standards. Not only is he a gifted author and editor, but he’s also a brother in Christ, a man of integrity, a veteran and a good friend. Check him out.