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An area I am currently looking to exploit is audiobook versions of my work. The problem I have is that most options, other than signing up with an audiobook publisher and forfeiting most of your rights, is to pay up front for the audiobook production and then hope that the ensuing sales yield a profit. From my preliminary research, I am getting the impression that audiobooks are a viable revenue stream for 'Indie authors' or authors wishing to maximise their royalty share by funding their own audio book production.
While ACX seems an intriguing prospect for US authors, it is not currently available to UK writers. The best alternative that I have found so far is http://www.dynamic-ram.co.uk. I had a sample produced by this outfit, along with a reasonable quote for services. If you are looking at opening up your books to a bigger audience, and you don't mind footing the bill yourself, I think that getting these guys to produce an audio book for you is likely to pay divends within less than a year (and then will make profits forever for as long as you leave the audiobook for sale.)
Writing has become very much like a business and I believe that audiobooks are a worthwhile investment in the same way as paying a decent editor and getting a proper artist to do you covers. It costs up front, but will more than pay for itself in the end.
I will keep you updated on what I do with my own books going forward, but for anyone trying to find the best route to getting audiobooks produced, I can personally vouch that these guys will do a decent job at a decent price, so keep them in your minds at the very least.