Hooking up an mp3 player to a stock radio.... just like old times..

I know what your gonna say: "get an FM transmitter", but those suck, especially in Los Angeles where nearly every station is spoken for..

So I was thinking about a FM modulator.. Basically a little box that you plug your mp3 player and antenna into, when you switch a switch it would turn off the antenna and bring in only the mp3 player audio.

That should work, right? Ive seen threads on this, but no one ever stated whether they got it working or not..

Or any other ideas? Besides the phone input.. mono sucks.