If you want to get more for free, try looking up free audiobooks. Audible is an obvious choice, but there are many other options. If you want to download a whole library of books, you can try Scribl, which lets you listen to new releases read by the author. These books are free, and you can find hundreds of them. Moreover, Scribl offers more stories than Audible, so you can download multiple books at once.
LibriVox is a nonprofit service that hosts a wide range of free audiobooks. These recordings are produced by volunteers, so they may be of variable audio quality, particularly in accents. In any case, LibriVox offers free audiobooks from public domain books. You can also find many recordings of public domain books on YouTube. While LibriVox has a disadvantage, its audiobooks are free to download and can be used however you want.
Then there is Thought Audio, which hosts free audiobooks by authors of various faiths. The site is funded through donations, and the volunteers read the audiobooks. The material can be listened to right on the website, or downloaded onto a computer. Thought Audio also hosts audiobooks by modern authors. Whether you're looking for a classic or a contemporary work, there is something to suit your interests. Then, when you're ready to download, you can listen to any audiobook from the website.
AudioFile Magazine has an annual summer reading marathon for teenagers called Sync. The program is not necessarily a marathon, but it allows participants to listen to two thematically linked audiobooks each week. They also have a trending book chart, where people can make recommendations for books they'd like to read. There are many more options than Sync, and they are definitely worth checking out. You'll be amazed at the variety of books available!