Check with some journalism departments and college newspapers—perhaps where you went to school—and chances are you'll be able to find several bright and eager candidates. Read some samples of their work. Maybe submit a sample chapter for editing. Ask faculty members for opinions. Then make the deal.
I was the copyeditor for the Brown and White student newspaper while a journalism major at Lehigh and did some editing of other students' term papers—but not books.
Roseliny Genao edited some of my early books while on the student newspaper at Baruch College of the City University of New York, and she later went on to MIT for an MBA. "Not too shabby" as Adam Sandler said.
Students' skill levels will vary, of course, and so will your needs and their prices. You can pay per hour or per project. Expect to pay more if you need major rewriting than just copyediting.
- A student who has a part-time job making minimum wage flipping burgers will probably be thrilled to earn $20 per hour, or $300 - $500 for a publishing project.
- The vile Outskirts Press charges 1.6 cents per word for copyediting.
- The vile Xlibris charges 1.1 to 1.3 cents per word for copyediting.
- BookBaby charges $7 per page for copyediting and $10 per page for line editing. The company estimates 250 words per page, so that works out to be about 3 or 4 cents per word.
As long as you're investigating colleges, consider hiring a professor, not just a student. If you're writing in a specialized field, it could be worthwhile to hire a faculty member to check your facts, and pay someone else to polish your prose. Different kinds of editors do different kinds of editing.
[photo of Dartmouth building came from Yahoo]