https://wolnelektury.pl/katalog/audiobooki/
Free, downloadable, and legal. Very good quality.
Audio library of required readings of Modern Poland Foundation. It is free of charge and you can use it without any limits. Audiobooks are recorded with the participation of famous Polish actors like Danuta Stenka or Jan Peszek.
Here's my favourite book:
Platon, Obrona Sokratesa
https://wolnelektury.pl/katalog/lektura ... audiobook/