If you are comfortable sailing the high seas: https://audiobookbay.is/member/login.php & soulseek.

For legal sources:

1. Audible
2. Scribd
3. Storytel (if available)
4. Overdrive/Libby
5. Apple Books
6. Google Books
7. Chirp

Not so legal sources:

1. Audiobookbay
2. Mobilism
3. Audiobb

I buy mine from Audible mostly then use a Windows app called OpenAudible to download, drm strip, and convert to a more usable format. It works, but you do need a copy of Windows and I think that Open Audible is a paid app.

I subscribed to Scribd years ago because I hated Amazon. Honestly, it has some minor inconveniences, like it’s shady estimates about the value of what you’ve consumed, but it by-and-large has the things I want to listen to. It’s like Netflix. Ain’t perfect but it works for me.

I’m fairly addicted to librivox, they’ve got all the classics and so many fascinating oddities. it can be hit and miss with the readers but also there are some brilliant ones.

My library uses Libby. For everything I acquire outside of the library, I use CloudBeats

I search for interesting books on Amazon or audible, and then buy them on Spotify. I stopped buying from audible because it tries to force you to subscribe rather than just buying single books.