It’s been years since I last paid for an Audible.com subscription. I just signed up this week ($5/month for 3 months) and it’s been a delight so far. I discovered that you can pretty easily remove the DRM on the audiobook .aax file. I am using Audible Tools to help me create the ffmpeg command to do this.
Another recent discovery is that Overcast, my podcast player of choice, seems to natively support .m4b files (audiobook file format). It even includes artwork and chapters, so it behaves just like most of the podcasts I listen to.