£7.99 gets you one book a month and also access to the Audible Plus catalogue which is 1000s of books free for members to listen to. you can get 24 credits for £109.99 if you pay annually (I do)I think...only think mind you...that for £7.99 a month you can choose one audiobook to own outright, but can stream other audiobooks as much as you like. Not 100% sure though.
Spotify's new audiobook service gives you 15 hours a month free listening and then you have to pay for additional listening hours.