Hopefully you don’t have “Audacity files”. that only play in Audacity. MP3’s or FLACs, etc.? WAV files will “play anywhere” but are not as good for “tagging” with artist/title/album information, and they are bigger since they are uncompressed,
Do you have a smart phone? Most newer cars can link to your phone via Bluetooth and you can play through the car radio. And most smart phones have plenty of space for lots of MP3s.
You’ll probably need some help if you haven’t done that before. (I haven’t done it… I have “iPod docks” in my two vehicles and about 18000 MP3s on my iPod Classic.)