My wife listens to audiobooks from the library when she is driving or running. Now that she drives a lot less, she has trouble getting through one before it expires. Audiobooks are very slow compared to reading.
She thought about audible but holy crap. No wonder they have so much money for advertising. Something like $10/month for up to one book and close to the same amount for each additional book.
Audible is indeed very expensive if you go beyond the 1 credit per month plan...although they do have offers where you can buy a few credits at a time and the cost goes down to $15 a book or so.
To just outright buy books some of them are $30-$40 which is just insane.