It's also important to note that editing is not just making sure your copy is grammatically correct -- that's called copyediting, and you can pay for that by the page. It's pretty easy to find a copyeditor.

A good editor is someone who knows good writing and will tell you if you're producing crap. They should also be able to tell you if you're writing to the current zeitgeist.

There's value to having good editorial support but, IMHO, it's not worth signing over all your rights and earning potential.

You can outsource all phases of editorial and production, the big houses already do.