I have seen aftermarket accessories that allow you to plug a cassette player into a car stereo that might solve your dilemma. Don't know the name of the product or the cost. Try an internet search.
I have a Samsung mesmerize phone And I'm wanting to play my phone music through my car speakers and need to know if that's possible. My car stereo does not Have an aux, Bluetooth, or cassette option. What can I do?