From what I know about Audible, it is a service providing audio books. If said audiobooks can be downloaded locally, then any media player will go. Otherwise, you'll need a device which supports Audible app (iPod, iPad, android phone / player), and Internet connection.
When you say "cheap" - what is your budged?
"Long battery life" does not mix with "Loud speakers". Yoou should look for two separate devices - player and speakers.