BigDeals via eBay offers the BlackBerry Seatbelt Bluetooth Speaker, model no. ACC-52983-001, for $17.99 with free shipping. Outside of the mention below, that's the lowest total price we could find by $11. It features a microUSB port, headset jack, volume and music controls, and the ability to connect to multiple devices at once. Deal ends July 6.
A close price: Park Deals via Amazon offers it for $18.99 with free shipping for Prime members.