I don't know, usually writer's hire
agents. Editors usually work for a publisher or a publication. I've never heard of freelance editors.
EDIT: And apparently freelance editors are thing.
Here is the
Editorial Freelancers Association webpage and their rates. Seems like they don't really consider games much. However, they do consider 250 words a "page" and for "Proofreading" they do 9-13 pgs an hour (so 2250 to 3250 words an hour) and they say the going rate for that is $30-$35 dollars an hour. "Substantive | line editing" (editing your word flow?) is only 1-6 pgs an hour (or 250 - 1500 script words an hour) for $50 - $60 an hour.
Holy banana boats - I'm in the wrong line of work. A novel length VN script - 70,000 words (or around a 150 page book), just proofreading would run you a minimum of $650 dollars. At the upper end of 150,000 words (around 300 pages) you're looking at $1615 dollars just to proofread your script. To really edit it you would need to pay them an
additional $6000.
I'm sorely tempted to claim editorial power and have your hire me based on two college degrees and growing up in a family of English teachers (and I'd only charge half!) but I think the amount of money being asked for is a little ridiculous, and I'll explain why:
1) Editors can proofread you, but so can friends or family. You can even proofread yourself. This is just going over your script and looking for grammatical mistakes and misspellings. Maybe making sure your tense stays the same or your don't mix up names. It just requires knowledge of grammar everyone should of learned in school coupled with slow methodical patience.
But this is perhaps the only place an editor might truly be valuable and save you time. If your grammar skills are weak or you have no patience, maybe the $600-$1000 dollars will be worth it to you. An editor should certainly be able to catch all your mistakes, but it seems unnecessary to have a professional do this.
2) Being an editor is SUBJECTIVE beyond the grammar and spelling. Yes, there are certain ways to word things to make them have more punch, or they can pick out plot holes, let you know when something isn't making sense or getting across, or when they got bored - but your friends and family can tell you the same things. Good editors are writers themselves - and every writer has a style of writing. If your style and the editor's don't match up . . . .
3) Editors don't always know good work when they see it, and don't always know bad work when they see it.
Harry Potter was rejected by 8 editors,
Animal Farm by 4 editors,
Twilight by 14 editors (make of that what you will), and
Lolita was rejected by nearly every editor, with one saying - “It is overwhelmingly nauseating, even to an enlightened Freudian. To the public, it will be revolting. It will not sell, and will do immeasurable harm to a growing reputation… I recommend that it be buried under a stone for a thousand years.” (It has sold over 50 million copies and made its author world famous, and in 57 years has never been out of print.)
Those stories all resonated with tens of millions of people, and editors told all those authors the writing and story was no good. What if you get an editor that doesn't like your kind of stories? Both
Lord of the Rings and
Harry Potter were rejected by editors all together - only seeing publication because a
child got hold of the manuscript in both cases and begged their parent with editorial power to publish!
At the end of the day you could have one editor completely happy with your work and another one suggesting major rewrites, and paying for the privilege!
I'm not suggesting an editor is worthless, but they certainly shouldn't be viewed as a panacea for all that ails your writing. Unless you are truly a horrible writer, I would suggest going with friends and family. Or a writing workshop. Or you could pay me.
(Because apparently I can qualify as an editor -
Editor Credentials and How to Check Them)
) 
.... Yeah, maybe I should change my major...
It's funny because my mother has a very prominent Southern accent. I never thought I picked up any of it, but when I was in the military I discovered that when I was several days sleep-deprived and stressed I would slip into a drawl! 
