I too have a Kindle Fire. I like audio books as well as reading. Watch out for the Kindle books which also offer the same book in audio at a cheaper rate than buying the audio alone.. Best of both worlds.
I get them from the library. Free! Perfect. Years ago audio books were on CDs or cassettes only. Nowadays they are available pre loaded on an MP3 player. All you need is a small battery to pop in and your own headphones/ear buds (health & safety) and you’re good to go! No messing about with discs.
I’ve just listed to a 17 hour book on one. They are only the size of a cigarette packet. Here’s a photo ...
I believe Local libraries do audio books I keep saying I'm going to find out how!
I have also have a Kindle Fire Ngaio If you check out Book Store it will have an offer for one months free trial of audiobooks. Just remember to cancel before the end of the month if you don't wish to continue.
On book store you will find a number of books for 99p sometimes there will be an audible box to tick and upgrade. I try to search audio for under £3 This still equates to £3.99. I believe audible subscription is about £7.99 per month.
I listen to radio plays and audio books which are free on youTube.
Just type into Google the genre you wish to listen to. Eg YouTube crime and mystery play or books