Right now you can pick up the Mpow Buckler, the company's latest waterproof Bluetooth speaker, for just $15 at Amazon with coupon code NJB5QCK7. It has an IPX4 rating, so it will work great by the pool, out camping and even in the shower with its suction cup. Each charge will score you around 8 hours of playback time, and it takes around 3 hours to charge it back up.
The speaker has a built-in mic to use it as a hands-free speakerphone as well. Remember, you will need to use coupon code NJB5QCK7 at checkout for the savings.