The Muzio Player App is a one off price.
Better if you try various phone apps for free until you find one that works for you. If you like it, then you can buy it if you wish.
Some can be very klunky to use. Muzio works for me.
Alternatively, just buy a usb key load it up with tunes an. Plug it into the usb port on your car. Point the car to the media player and it will play your tunes