What would Romo's trade value be if for some insane reason it came to that?

Not implying we should trade Romo or that it's very likely at all, but there is a small (5%?) chance that Dak balls out and flat out takes Romo's job. If that were to happen, would trading Romo be the most reasonable thing to do? You can't really have a $20 mil/year backup can you? Just thought it was a fun topic to explore in this little dead zone before the season kicks off.