I'm not sure who told you it will be too expensive, but it will definitely be a new design issue.
An analog TV signal was actually two separate signals; an AM video signal and an FM audio signal. The audio was not unlike an FM radio station. Also, in North America, FM radio is between TV channels 4 and 5. So, for a manufacturer to add TV audio to a radio, all they really had to do was expand the tuning range.
Digital TV is a whole other animal. Digital TV is a steam of data that contains many sub streams, multiple videos, multiple audios, data, closed captions, some overhead to organize everything, etc. To recover the audio, one would have to pretty much add the entire decoding section of a DTV, minus the screen. Plus, the user interface would have to be modified because, once a signal was decoded, the user would need some way to select which audio stream for listening. This would not be cost prohibitive, but it would add significant cost to the device.
Broadcast Engineer for 30 years.