This isn't a bad question, and it is a problem. TBH, I'm not sure how to get around it, either. That being said, the normal places you'd go for this kind of thing is the 800lb gorilla: Elance.
The trouble with this is that most clients (the ones buying freelancer services) are price-buyers. That is, all they care about is how cheap they can get someone to do X or Y. Quality is a distant second or third consideration. That means a lot of the freelancers that are drawn to places like Elance aren't very good. (Because the good ones have a steady stream of work, or work for someone else.) You can't really expect high quality work when you're paying crap wages. 396
(The equivalent of $10/hr isn't enough to entice anyone but the really desperate, or people who live in other countries whose primary language isn't English.)
All the same, you don't have enough work to justify contacting a translation agency, and you don't have the funding to post a job ad on a quality board. (Writers.StackExchange doesn't have a careers section like StackOverflow.) So that leaves you with creative approaches to getting quality people.
1. Contact an English professor at a US university, explain your situation and ask if s/he's aware of any talented students that might be interested in doing some editing.
2. Post on Craigslist, and be completely open about what you can afford to pay.
3. Look at some of the top posters here, and see if they have contact information in their profiles, and email a few of them, and explain how you found them, and be open about what you can afford to pay.
4. Whatever else you can think of
The problem with these approaches is credibility, particularly because people are rightly skeptical of overseas work with Sakawa being so prevalent, so be prepared to be rejected quite a bit, and be prepared to have to make a substantial up-front, good-faith deposit before getting someone to commit. Be prepared to lose a bit of money if people bail on you. (These are mitigated a bit with approach #1 and #3.)
Good luck! 897