I'm a native English speaker, with niche written copy published in print and online. I'm not your cheapest bidder, but then again given the nature of your specification requiring exacting grammatical perfection for somebody in the writing profession, you might be better of working with somebody who actually is English.
Compared to the other bids I can see so far, I think I'm offering you the greatest quality of written English at present. Please review Private Message for examples of my work.
Arron