Reddit reviews Thru-Hiking Will Break Your Heart: An Adventure on the Pacific Crest Trail

The best "Standard" deal is the
Platinum Annual
24 Credits/Yr.
You pay $9.57 per credit
$229.50 per year

That's always available and offers the most credits at the cheapest price per credit.

If you follow the Audible sub then you'll find signup deals on there from time to time. The last I took advantage of was the
Discount Gold Annual
12 Credits/Yr.
~$8.29 per credit
$99.50 a year

You could sign up for that one until April 5th. Sometimes if you call and ask you can still sign up for one of these deals, but I haven't done/tried that so I can't say much about it. I don't know of any sign-up deals going on right now, they usually happen around holidays.

Depending on the genres you enjoy, your best bang for your buck might be a Kindle Unlimited subscription and then picking up some cheap audiobooks through whispersync. You can pick up a KU subscription for $0.99 for two months (https://www.techbargains.com/deals/amazon-kindle-unlimited-membership) and if you hunt around you can find a bunch of good books for $1.99. It's mostly Sci-Fi and Fantasy, but as a few examples:
https://www.amazon.com/Are-Legion-Bob-Bobiverse-Book-ebook/dp/B01LWAESYQ
https://www.amazon.com/dp/B01MFGX5GI/
https://www.amazon.com/dp/B00SLWQGUM/
https://www.amazon.com/Thru-Hiking-Will-Break-Your-Heart-ebook/dp/B00W4RICAM

Those aren't endorsements, just examples (I've only read the first one, which I would endorse if you like Sci-Fi)

Beyond that if you like classics you can usually find some of those cheap:
https://www.audible.com/pd/Siddhartha-Audiobook/B07HK6JZSC

On occasion, if you go to cancel your subscription you'll be offered a deal to keep it. I haven't signed up for any of those, and don't know what those deals are, but it's an option.

Last but not least, you can just buy more credits. If you've run out of credits (or if you contact Audible Support) you can usually buy 3 credits for $36 ( I think that's the correct amount). I generally wouldn't recommend this option, it's a bit more expensive to buy the Gold Plan, but you get a year's membership with that. Whereas buying credits straight out still leaves you paying a monthly subscription as well.

Before hiking in 2016, I read Thru Hiking Will Break Your Heart and Hiker Trash both of which I thought presented accurate descriptions for what it's really like to hike the PCT. Not the most thrilling reads, but worth it if you're considering doing the PCT.

The two you've found are great first reads. Definitely pick those up!

Are you interested in stories as well as tips? I really enjoyed "Thru-hiking will break your heart" by Carrot Quinn.

Cam Honan has a book list you might check out: http://www.thehikinglife.com/resources/books-for-hikers-and-backpackers/

Novel:
https://www.amazon.com/Thru-Hiking-Will-Break-Your-Heart-ebook/dp/B00W4RICAM

Informational:
https://www.amazon.com/Backpacker-Long-Trails-Mastering-Thru-Hike/dp/1493028723/