Park Deals via Amazon offers Prime members the BlackBerry Seatbelt Bluetooth Speaker, model no. ACC-52983-001, for $12.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping adds $6.39.) Outside of the mention below, that's the lowest total price we could find by $30. It features a microUSB port, 3.5mm port, volume and music controls, microphone, and the ability to connect to multiple devices at once.
A close price: Big Deals via eBay offers it for $14.99 with free shipping.