From the description of the book as being the 'ultimate' and the very short deadline, I would suspect this is more a call for proofreading rather than editing. Most of the time when someone believes they've created the ultimate of something they just want someone else to make sure they've spelled everything correctly, not really for input on ideas, flow and such. As well, I wonder at how many hours the writer thinks it will take to edit that many pages. I know one of the folks that recently asked me to work on a 300 page manuscript assumed I could edit about 30 pages an hour and had budgeted 10 hours worth of pay. They were very surprised when I very seriously informed them that 30 pages an hour was NOT reasonable for any kind of decent editing, even proofreading that fast is ridiculous unless all they want is the very worst of the edges whacked off.
This is only an opinion, but it is my gut impression that there would need to be quite a bit of negotiating and setting of expectations in this situation.
~J