This $13 dual USB car charger also has Bluetooth and is an FM transmitter
(Windows Phone Central)

Grab one for each of your vehicles. Using coupon code VIVAFF22 during checkout drops the price of Anker`s Roav SmartCharge car charger with built-in Bluetooth / FM Transmitter down to just $12.99. This is $7 less than what it normally sells for, and a huge discount compared to buying the two components of it as separate devices. It comes equipped with two PowerIQ USB ports to charge your devices while on the go, and it has dedicated buttons to answer calls, and skip forward and backwards while listening to music. You can connect your phone directly to it via Bluetooth to stream music with ease, and the FM transmitter portion allows you to play it through your car`s speaker system. Anker backs it with a 12-month worry-free guarantee. See at Amazon ...