There are lots of Bluetooth transmitters on eBay and Amazon. I use one with a Bluetooth speaker to monitor a shack radio elsewhere in the house. Note, some small transmitters have a short battery life of around 5 hours.
Some handhelds with Bluetooth may work with the built-in car Bluetooth system, although I’ve not had any success pairing an AnyTone D878UV with a VW Group car.
73 Dave