I just finished the fifth edit of my book.  This was the final edit before it goes to press next month.
I payed two different professionals $250 and $500 to review my book for content and structure. But even after making all their changes and corrections I had to review my book two addtional times myself.
The forth edit, I read, primarily, for content, flow and consistency correcting grammatical errors as I found them.  This fifth edit was a time to realize that the book was finished and only grammatical and formatting issues could be addressed.

Here is the saga of my editing cycle (which took longer than writing the book):

Professional Edit 1: 65000 words…summary of 19 page critique “dig deeper…I want to know more…I don’t understand the ending”

I thought I needed more feedback from a different objective source so I took it to another pro.

Professional Edit 2a: 65,000 words…summary of 1 hour dialog and 20 page critique “Characters need more motivation…I want to know more…I love the ending but it needs to be fleshed out”

I revised the book based upon both editors comments adding two new characters and 28,000 words then I resubmitted to edtor 2.

Professional Edit 2b: 92,000 words…summary of comments “The two added characters accomplished their purpose and provided a real sense of intrigue.  Everything flows and I found myself compelled to turn the page to see how this would end.  Once at the end, I was not disappointed.  It was like you were in my head answering all my questions.”

Personal Edit 1: 
5 errors in consistency (Changed character names, but not throughout book)
21 Homophones (right sound wrong word: hear, there, etc)
14 sentence reworks (just wanted better phraseology)

Personal Edit 2:
5 Publisher formatting errors (improper spacing)
3 errorneous paragraph breaks
3 homophones missed in the first edit
3 phrase corrections
3 inconsistent capitalization
8 missing words (just left words out of sentences, a, the, etc)
11 mispelled words

At this point it’s going to cost me about $100 to make the corrections in the publishers proof, but I am content to pay this. I could have paid another professional editor .012 cents a word  ($1104) to find about 2 dozen of these errors and probably another dozen or so that I have missed.  But I am satisfied that the four edits I have undertaken at a total cost of $850 are sufficient to put this edition to bed.

The last reading was by far the hardest.  It’s so easy to make changes when you are E-publishing you could very easily edit forever, but there comes a time when you must let go and trust that you have labored enough to reward readers exponentially for investing their precious time in your work.