Ugh! I've tried this one, too, and it's a spectacular failure. I chose to try out this format on my best-selling book, Beyond All Price. My choice of a production company was ACX, the Amazon affiliate, because they handle the contracts between author and narrator and do all the final formatting. I got to audition several possible readers and selected a talented and experienced woman who seemed to be a perfect fit. And she agreed to do the job on the basis of a 50/50 royalty split. If I had had to pay her on an hourly basis, the cost would have run into several thousand dollars. The project stretched out for over nine months because the narrator had other paying gigs and concerts (she was also a professional singer) that took up her time. The whole thing was easy for me. All I had to do was listen to the tapes at the end to make sure there were no obvious errors, and I think we ended up with a great product.
However, it simply has not sold. My readers are not the kind of folks who listen to audio books, apparently. They don't drive cross-country, or go to the gym or do other mindless things that would give then the time to listen. If they travel by car, they also have a spouse and children who aren't interested in historical biographies. (Beyond All Price runs for over 13 hours.)
ACX sent the narrator and me 75 code numbers apiece; those numbers could be exchanged for free copies. The idea was to distribute them to our friends so they would write reviews for the website. I soon learned that I couldn't give the audio versions away, even by running contests and stuff. I still have over 50 left. My narrator had the same problem. And then we realized that we would receive no royalties on those give-away copies. So we were exhausting our small readership by giving the product away. The result after six months of publication? There are exactly 16 copies in circulation, and the narrator and I have each received payments of approximately $50.00 total. I feel really bad for the narrator because she did all that work for free. At least I only spent a few hours on the project. But I'll never do another one.
Maybe it's a great idea and I just did a lousy job of marketing. Maybe I don't really believe in audio books (I've never purchased or listened to one), and if you don't believe in something, you can't sell it. Maybe I'm just an old fuddy-duddy who's stuck in a rut, but I've gone back to writing the next book, where I know what I'm doing.