The Amazon Tap has always been a solid option for a portable Bluetooth speaker, especially since it has all the functionality of the Echo and Echo Dot. The speaker has occasionally dropped in price since it was released, but this is the lowest it's been yet - $79.99. That's a whopping $50 off the MSRP.
If you're completely unfamiliar with the Tap, it's essentially a more portable version of the Amazon Echo. It's a tall circular speaker with hands-free Alexa (so you don't have to press a button before you start talking, you just say "Alexa"). When you're away from a Wi-Fi connection, it works as a normal Bluetooth speaker, with an estimated 8-9 hours of continuous playback. Amazon also sells an optional 'Tap Sling' that protects it against bumps and drops.
You can buy the Echo Tap at the source link below. Again, this sale is only for one day, so don't wait too long.