Boxnovo via Amazon offers the Aroccom Waterproof Bluetooth Wireless Speaker for $39.99. Coupon code "AROCCOMB" drops it to $28.99. Plus, Prime members bag free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.91.) That's a buck under our December mention, $31 off list, and the lowest total price we could find. It features playing time up to eight hours and has a rechargeable lithium-ion battery.