Martina and I were just talking about this topic recently. Freelance editors come at a hefty price, but literary agent Rachelle Gardner seems to make the case on her blog that they can be a very valuable asset if used properly. Maybe you've been considering contacting one. Check out her post today before you go any further. It may help you make the call a little bit easier.
If you're a member of SCBWI, you can access a list of freelance editors by logging into the website and going to the publication guide. Freelance editors can be found under the directories and resources section.