I am terribly fortunate to have made the acquaintance of a well-published author (Mindy Klasky -- publicity for her won't hurt) before she was published, and we have traded chapters for years. I hadn't realized before how lucky I am. I have proofread about 14 of her novels, and she's done about 12 of mine. I've gotten to where I enjoy the process of analyzing every paragraph as I read. It's ruined me for poorly edited books, though.
Just today I read two chapters out loud to a woman I bought lunch for. Fortunately, she enjoys my writing, but I brought home sixteen pages with marks on them. Drunkenvoltaire is right; reading out loud to an audience really makes errors stand out.
None of which helps you much, unless you can make friends with someone literate, or find a decent writer's group and trade editing.
I would suggest that you ponder maybe putting up the first chapter or two and letting the community chew at it (brave soul!) because I've read the "Look Inside" for many books that have made me holler at their errors. It's your best foot forward; those first few chapters really have to be polished.
If you would like to contact me via my website ( www.davidwaine.net ) I will send you full details of how I edit my books comprehensively, and no, I won't charge you for it. You should then be able to do most of it yourself, although you will still need someone you can trust to proofread it for you. That is a job that cannot be done by the author because he / she is simply too close to it.