This is an interview at Joe Konrath's blog with an editor he has used and liked in the past. She's offering services ranging from basic proofreaching to a full edit, with prices ranging from $25 to $40 an hour. The proofreader I used, who I recommend heartily, charges $25 an hour. So, again, if you want to hire someone, that's your ballpark figure. Anyone quoting far higher prices needs to be treated with extreme caution.