Do you mean 300 page?
Proofreading ain't rocket science and if you plan a career as a writer you learn the basics. Don't go throwing money out on proofing. You'll never make it back again in sales.
Get a copy of Strunk and White's
Elements of Style. Most libraries have it, and used bookstores have them by the dozen.
Every pro writer will have that book on or near their desk.
Read it and apply what's in it. It's pretty easy.
Use your spell check, fully aware it may insert errors.
Then print a hard copy.
Read the book aloud to yourself. It's easier to spot errors that way.
And get a trusted friend to read it. Tell them to circle every last error they can find.
Cost to you? The price of
Elements of Style.
No agent or editor expects to see a perfectly clean, error-free submission. They do expect you to make an effort. I'd seen some beautifully turned out submissions--but the writing was not something I could buy. I've seen some horrible looking subs by people who didn't bother with even the spell check--no excuse for that these days. I sent the sub back asking them to clean up the MS and try me again.
It's not hard to be a pro!
The plain fact is however clean a sub is, the words have to be worth buying. If they come back to you, then rewrite and keep submitting.
In the meanwhile, you work on another novel to keep your head from exploding!
If, after you teach yourself the 101 on self-editing, you still think you need to hire a copy editing service, be aware there are sharks in the pool. Some call themselves "Book Doctors" and the like. Always check
Preditors and Editors, or Google the name + "scam" or "ripoff" to keep safe. Run the name through AW's Bewares and Background Checks. Lots of sharks prey on would-be writers, offering any number of useless "services."
Don't believe websites that say you HAVE to have an error-free manuscript or it will get rejected. That's horse hockey. It that was true, nothing would ever get published.
Just give your stuff the kind of going over your 5th grade English teacher would give it. That should take care of things just fine!
