In the confusing battle between Amazon and Hachette, Amazon has an army at its back made of self-published ebooks on offer for reasonable prices. With the rise in these, I haven't seen an equal rise in publicized freelance editorial opportunities. I think there is a misunderstanding between the traditionally published and the self-published about what an editor does, and it's not just to correct your spelling and grammatical errors, though that helps.
I am no opponent of self-published books -- my background includes a couple and I like some. But for every work like Hugh Howey's sublime "Wool" series, there are probably 100 books with derivative plots or poor proofreading, that are burdened with trite phrasing, contain obstructive pacing and structure issues. More to the point, there are a 100 books that are varying degrees of unreadable.
I have given up on more self-published efforts than I've stuck with, for different reasons depending on the book. Maybe the characters of a dystopian society in the far flung future keep slipping in some current trendy slang that is too distracting. Maybe it's because a science fiction story goes into info-dump mode for chapters at a time, ignoring the characters that made it interesting at first.
Some of these books are on the generous end of the unreadability scale. They are almost there, but could use some final finesse to take it from a work that has good things going for it to a work people would want to devote time to.
In some, you imagine it all starts at the beginning -- derivative plots. I've slogged through too many book descriptions that are about trendy scenarios like earth after apocalypse or some dystopian future, but with no interesting variation on these well-trod areas. If you start out a book without much personal vision, I think it is going to be hard for an editor to bring any out of the clutter.
The editorial process begins after you've already written several drafts yourself. An editor is likely to require several more to get it from what seems good to what is good. It's a strenuous process, emotional and often taxing. It is not for everyone, certainly not for those with easily hurt feelings or too much of an ego.
I'm not saying don't self-publish. Do self-publish, just don't fool yourself. The truth is that despite the big press some self-published authors get, their success is a tiny minority. Those authors count as aberrations. It's hard enough to make a living through traditionally published books and, unlike those, the horrible quality of one self-published book can affect the perception of another. I've never met anyone who said, "That professionally published book was awful, I'm never reading anything from a New York publisher again." But I've heard it said about self-published books.
Looking at self-published book sales, Hugh Howey said that people always give higher ratings to a passable $10 steak than a passable $40 steak. That's the question, though. Is your ultimate goal to be a $10 steak?
My advice to a self-publisher: Take your manuscript as far as you think it can go, and then find a good editor to help you take it further than you imagined. Then self-publish.