Does anyone know a good editing company that will edit a book that I am writing for grammatical errors?

If all you're looking for is grammatical errors, give it to a friend with a good eye for grammar and usage. Professional editing services charge by the hour, and they're not cheap. I don't recommend a professional editing service until you're at the final draft stage and on the verge of publication. When you get to that point, go to the library and pick up the current issue of Poets & Writers magazine, where you'll find reputable (but pricy) editorial services advertized throughout.