Anything from ten an hour to 200 an hour and up, depending how good the editor is. Too many variables like location and ability level to really say.
Maybe the way to do this is to figure the cost based on your OWN hourly rate and how long you think it takes you to edit something like this, make that amount be what you offer, see who's willing to cut it for that much?
You're going to be putting the reputation of your business in the hands of some stranger; this may not be the time to go trolling Craigs List for bottom-feeders. What you want is a relationship with a capable peer, and that means you have to pay them about what you'd pay yourself for the job.