I use FreeCommander for things like this.  It has a flat view that lets you view all the files in all folders - and you can filter it.

Another very nice, and EASY audiobook/mp3 player is Simple Audiobook Player
https://play.google.com/store/apps/details?id=mdmt.sabp.free

I put this on one of those teeny Unihertz Atom smartphones for the person to use for audiobooks and he absolutely loves it.  Those phones are full smartphones but about as big as a pager.  This Simple Audiobook Player has big buttons and is configurable.  No ads, either.  It's rather nice.  And the interface is big and clear with no glitz.

@x16wda - well, yeah, the interface mainly.  For one, it has it's GREAT BIG NAME AND VERSION NUMBER embedded in the main window.  Who needs that there?  Version number is in the title bar already. 

I really hate ribbons.  Good ole' Menus and Toolbars are what I crave.  Menus cram all the commands into one place organized by their main topic (their name on the main toolbar) so it's super easy to go through and find all the commands you want.  With ribbons, you have to and look at everything and decide what it is before you use it.  (I know, I'm nit-picking).  At least you can hide the ribbon until you actually need it.

I do wish it would display large icons instead of just small ones for it's toolbars.  I'm starting to get old.



It *does* have a lot of versatility, though, and is most likely the best program in this thread so far.
Actually, I think I'll start using this program.