If you are serious and you have a factory or aftermarket radio, it is actually quite simple to play podcasts through your radio. I had the same problem with my 2004 Ford Expedition - there was no auxiliary input to the radio.
You need to be a bit mechanically inclined to do this, but it is easy.
You need an "FM antenna bypass modulator." It's a small box with an antenna input, an antenna output, and an audio input. You unplug your antenna wire from your car radio, then plug the antenna wire into the modulator and plug the modulator into the car radio antenna input. You then send your audio signal to the modulator. You tune your car radio to the frequency the modulator is sending out. Bingo -- you have audio from your device playing on your car radio.
I don't remember what brand I bought (that Expedition is long gone). But you can find them on Amazon for about $30. See: iSimple IS31 Antenna Bypass FM Modulator for Factory or Aftermarket Car Radios.
Apple dropped the 3.5 mm headphone jack from the iPhones, so you'll need a way to get audio out of the phone into the modulator. The easiest and cheapest way to do that is buy a Apple Lightning to 3.5 mm Headphone Jack Adapter.
Also get a 6 foot extension cable (3.5 mm female x 3.5 mm male) to run from the car radio to your phone. When I had my rig running, all I had to do was pick up the extension wire on the floor, plug it into the phone, tune the radio to the correct FM station and I was off to the races.
