You can get an FM transmitter if your car stereo has an FM radio.
Here is an example of an FM transmitter: http://www.amazon.com/gp/product/B0018P7WZ2?ie=UTF8&tag=johsgamsto-20&linkCode=xm2&camp=1789&creativeASIN=B0018P7WZ2
If your car uses a tape deck, you can use a tape deck adapter for your car stereo.
Like this one, http://www.amazon.com/gp/product/B00070FIAK?ie=UTF8&tag=johsgamsto-20&linkCode=xm2&camp=1789&creativeASIN=B00070FIAK
Indeed, the cable seem like the best choice, but make sure the jack on your stereo is not a headphone jack for plugging in headphones instead of MP3 and CD players.
went and got this. a little more then what I wanted to pay but I felt it would last. and I was able to quickly ask the company if it worked with my car and it does.