$25 for this DOSS waterproof bluetooth speaker. I have one, I like it, and it works on the hobie. I picked this over the others because it has sturdy mount points. you can clip it or hang it or whatever.
It floats temporarily, has great sound, plays music from bluetooth or a built-in sd card (via a crude/simple interface), and it has lights (which I appreciate a great deal when I stay out too late and didn't think about a flashlight or headlamp).
https://www.amazon.com/DOSS-Bluetooth-W ... way&sr=8-5but mostly: strong mount points.