Not what you asked for, but if you're interested at all in digital audio books, I cannot recommend highly enough Chirp Books. They use a flash sale kind of model, and sometimes the author you're interested in has their books at 90% off for like 30 days, and it cycles on rotation. You do need their proprietary player app to listen, but you can download the audiobooks to your device for offline listening.

For actual ebooks, you could look into your local library, and what schemes are available for 'digital lending'. Some platforms exist that let you loan movies, games, stream music and download ebooks using your local library card.