If you are hunting for a site like Tuebl, there simply isn't any. Most sites won't bother with audio because of the massive size of the files and bandwidth costs. It would cost a site too much to be an audio site like that. If there is one, you can bet they will charge to make up the cost of bandwidth because they are charged for it.
The closest you are going to get to that will be You are not allowed to view links.
The monthly fee cost isn't bad at 14 dollars considering it allows you to download your choice and most of the books I pick are listed for much more than 14 dollars.
If you want audio the only thing I can suggest is trying the torrent files. That requires utorrent or the like and searching places like You are not allowed to view links.
for audio book files. Simply type in the name of the book and it should pop up. Search like google works if you type Audio with the name of the book also for torrents.