Correct the grammar of a 15,000 word article

I have a 15,000 word article about London. It has been auto spun by a computer program, so the grammar is not good enough to use.
I need the grammar corrected into perfect English (I am looking for a high quality re-write).
The bidder needs to tell me how many hours it will take (my personal speed is about 8 hours approx if I do this properly myself).
If the bidder is successful and interested in more similar work, then I am happy to make this a weekly long term contract, as I can spin more words about London for future contracts