The Digital Pavilion via eBay offers the Urge Basics Soundbrick Bluetooth Stereo Speaker
in five colors (Pink pictured) for $39.95
with free shipping
. That's the lowest total price we could find outside of the mention below by $20, although we saw it for a buck less last week. It features a built-in microphone, up to 80 hours of usage per charge, Bluetooth 2.0, and compatibility with most Bluetooth-enabled devices (including the iPad and Samsung Galaxy Tab).
A close price: cyclopscase via eBay has it in Pink or White for pennies more.