Blutek via eBay offers the JBL Flip 3 Bluetooth Wireless Speaker in Black, Blue, or Red for $79 with free shipping. That's the lowest total price we could find by $21, outside the offers below. (For further comparison, in November we saw it for $3 less.) It features a 3,000mAh rechargeable Li-ion battery, waterproof casing, and up 10 hours of playtime per charge.
A couple of close prices: Electronics Expo via Walmart offers it in Red for $79.95 with free shipping, and Direct Deals To You via Amazon has it in Black for $82 with free shipping.