Touchscreen not working - dealer said radio?

We have a 2011 Prius (so not under warranty). Recently our touchscreen stopped responding to touch - we can still control radio volume from the steering wheel buttons, and the GPS is updating the map correctly as we drive, we just can't control any functions that require the screen, like using the CD player or putting in an address to get directions.

We've dropped it at the dealer, and they left a message saying the problem was the radio itself, and the radio needed replaced. Does that seem right? The radio _plays_ fine, and we can switch between stations using the steering wheel. That said, I don't know anything about the interaction of all of these things.

What should I expect them to charge me to replace the radio?

Thanks for any help!