Hi Mike. Question....How fast do you speak? I haven't done any audiobooks, but I have done narrations and it really depends upon the mood of the text, the characters in the book, and so on. What I suggest is to time yourself reading at least 5 pages and then do some math to come up with an "average" time per page. I emphasize that this is only going to be an average and having seen the actual script-book- whatever, will help you to adjust the time element and come up with a better estimation. I hope someone might have a better answer, but this should get you started. Break a leg !
What Barry says is true, although that is how long it will take to record the raw audio. I recently recorded my first audio book, and the company estimated the length of finished audio at ten and a half hours. I ended up with about thirty to thirty five hours of work, including the initial (non-recorded) read to familiarize myself with the book, the actual recording of the book, and editing of the audio. There was also an hour or two of pick-ups (no matter how careful you are, you'll miss something). My book was about 325 pages in length. I know this is late, but maybe it'll be helpful for someone else.