I first discovered these wonderful stories some years ago on this website
AudioBooksForFree.com
Princess of Mars
Gods of Mars
Warlord of Mars
Thuvia Maid of Mars
They are abridged and read by Grover Gardner and are FREE in a low-quality format but will give you a good feel for this other-world. Good to listen to in the car when one can't (or shouldn't) be reading while driving!! If you are a Robert A. Heinlein fan, you will enjoy the references to Barsoom in his "Number of the Beast".
If you get into Edgar Rice Burroughs, the same website also has some of the Tarzan stories
Tarzan of the Apes
Return of Tarzan
Beasts of Tarzan
All highly recommended for fun and adventure.
Thanks for making these books available, HarryT!