Is this behind the counter that you control?

or will these be positioned for custoemr interaction?

If it's behind the counter than a cheap Android phone coupled with an external hard drive is your cheapest bet.

Buy a Moto E or Moto G (I got a locked to Verizon Moto Elast week for $29.99) , buy a USB cable http://www.amazon.com/eForCity-Adapter-compatible-Samsung-Galaxy/dp/B00871Q5PI/ref=sr_1_1?tag=at88-20&ie=UTF8&qid=1415604596&sr=8-1&keywords=usb+otg, an external HD and

http://www.androidauthority.com/connect-usb-flash-drive-android-566239/


OR, buy a DNLA/Streaming network hard drive http://www.amazon.com/Cloud-WDBCTL0030HWT-3TB-Personal-Storage/dp/B00EVVGAC6 and use it to store and stream the music.