A really simple solution to building a Network controlled MP3 player.
The project utilizes the ESP8266 module, I am using a Wemos D1 mini that is really inexpensive (typically less then $5). The MP3 player is available from various supplier on eBay and AliExpress and again typically cost less then $5, AliExpress seems to be cheaper. I paid $3.08 for the one I got from AliExpress.