You can find quite a choice by searching online. The trick is to know who is good, and are their charges reasonable.
To find out who is good, prepare a sample text of a page or two and send it out to a shortlist of likely candidates to edit.
Most good and busy copyeditors may refuse to do this on spec, so be prepared to offer to pay—it may cost you a bit, but if you need a copyeditor on a regular basis, or for an important book, it’s worth the investment.
However, I routinely do such on-spec editing when preparing cost estimates for new clients, because unlike many editors, I charge on a sliding scale, based on the amount of changes done to the text (since it stands to reason and is only fair that someone whose text is well-written should pay less than someone whose text needs a lot of work). It also makes my charging calculation transparent, so the client knows that I’m not plucking the word rate out of the air:
(I then repeat this procedure for the entire work at the end, to calculate the cost, as in the above example).
If you find someone who does a good job and charges in similarly transparent fashion, you can be reasonably sure that you’ve found a good copy editor—and when you do, hold on to them, because like a good wine or a Rolls Royces, they only get better with age.