First, decide whether your time or your money is worth more to you right now. You can greatly reduce the amount of money your project will cost by investing more time, and vice versa. If time is no object, you may want to spend some hours in the library reading style manuals and going through your manuscript with a fine-toothed comb so that when you do hire an editor, (s)he will be able to zip through it quickly. If you end up deciding that’s more effort than you want to invest, then you will at least find the monetary cost of hiring someone to do it for you a less bitter pill to swallow.
The price you’re going to pay an editor depends on a lot of different factors. You may just want an editor to proofread your book to catch minor errors and typos. Or you may want to work with an editor to help you overhaul your book. Getting familiar with the kind of editing options available will help you choose the right editor. Typical book editing services are:
Work in house first. That’s the best way to learn all you can about editing and proofreading and make good connections. I have met several people I’ve worked with from hanging out in Twitter and responding to tweets asking for an editor or proofreader, but I have had the most success from business connections I made while working in in house. Other things – a web site, professional associations such as the SFEP and the EFA (though I can’t say much more on these as I am not a member of either yet!), social media.
I hope this helps! Please don’t be discouraged by editor’s rates. Many of them do this full time or to supplement their other income with their business. The quality of service is not necessarily tied to project cost, but hiring anyone who is a contractor or freelancer often means you’re getting one-on-one personalized attention you might not get if you worked with, say, just the editor of a publisher who could see your book as a quota to fill. Just my two cents!
Obviously there is a big difference. I actually started with screenplays (with some mild success) partly due to hearing that as long as you have a good story, the grammatical errors won’t be a big deal. Well, that was not true. Maybe if a producer liked the story or I was already established but every contest I entered always came back with feedback about the grammatical errors. Even if I won or placed as a finalist, I always received critique on that. Very little is spelling error, it was more about structure, etc.