I've had an Audible subscription for a long time, but you don't really own the content. I found a way to download and unlock the content and as soon as I've used up all my credits, I'll cancel it.

Spotify has an audiobook program, but there was mention a few days ago that they have changed their terms and conditions to mess with the content rights of authors. They also have this strange metering system where as part of the service you get so many hours of listening and then have to purchase additional credits to finish the book, or wait until next billing cycle.

Libby and Hoopla are both tied to public libraries and are free, but you have to put holds on popular audiobooks and wait.

Another interesting service is Kobo: https://www.kobo.com/us/en/plus. They have an all-you-can eat plan for audiobooks as well as ebooks+audiobooks. I haven't used them, but will after I cancel Audible.

There are services like https://audie.ai/ that use AI to turn textbooks into audiobooks. There are a lot of them out there. Most are targeted at authors or publishers, but there are also projects to convert Project Guttenberg books into audiobooks: https://www.csail.mit.edu/news/ai-generates-thousands-free-audiobooks