The price increase just from FM to DAB is huge, let alone when you consider that my radio has better sound quality than most, and plays MP3's OGG etc. Ridiculous prices
That said, you can get a DAB FM Transmitter for your car. You use the DAB radio to choose a station, which then transmits over FM to your Car radio.
The question is, do you want to run an extra bit of kit (which is also far easier to nick as it's jsut suckered onto the windscreen a la satnav)? I'm buggered if I'm carrying that and my satnav whenever I get out of the car, so given the choice I'll just have to give radio a miss (until prices come down).
Even fitting them in new cars won't do for me, even if I had the money to buy a new car, I'd probably want to move my Half Decent(TM) sound system across to the new car and replace the shitty system that is often in as standard.