Need help with little sound player

As a cosplay project of mine, I want to build a small version of GLaDOS that plays a voiceline when i press a button. I have a working Python script that plays a random mp3 when I press space. I saw something about a raspberry thing that I can connect a battery, speaker and button to, but I dont know what parts I would need or how to connect them. I'm tryna keep everything as cheap and light-weighted as possible. Could use some help :P