We went on a LONG car trip this weekend. Unfortunately, the audio book we listened to was not really approved for all listeners (however, the concerning ones slept through the questionable parts). It was a fun and fairly spontaneous trip. It did remind me how great it is to have lots of listening options on hand. Here are some free or cheaper resources for audio books (many are in the public domain, some have volunteer readers which can be hit or miss).
Librivox - This is my go to location. Most readers are pretty good - just listen for a minute before you download. Your kids will memorize the little intro that goes with all of these recordings - but FREE. If you looked at the Ambleside list last week and wondered what was available on audio - here is your connection.
Sparkle Stories - This is a free app that has stories for younger children (4 to 8). They focus on stories that have cooperation and teamwork and stay away from scarier themes for children. I haven't really listened (my kids like the scary stuff) but many friends recommend it. If you are interested use the trial and see if your kids like the stories.
Lit2Go - This website also features primarily older books but most of them have some acknowledged literary value. Ambleside records MANY things - this is a more curated (I can't believe I just used that word) listing of stories. They also have it available in PDF and easy to read on screen as you listen - this might be good for kids who are just learning to read.
Of course, we all know about the wonders of your local library and remember that if your library has Overdrive you can use it to check out audio books without leaving your house! Audible is the most well known pay service. I have yet to use it but here are some tips for getting the most out of it (here, here and here).
I am sure that there are more services (and some that we used to use that I can't seem to find anymore - bummer). I imagine there is a whole world of podcasts that deals with this subject too - but I haven't delved into it. If you have places you like to go for free or cheap audio books for kids - let us know!