No idea if it is cheaper to move a 6 lane road and/or another road plus buildings.
The airport is "grown in" - used to be in the green fields and is now surrounded by the city...
We are trying to have another airport build (an old US Base would readily be available, 2000mtrs runway with 2 ILSes without overflying habitated areas) but in todays climate in Germany I reckon the reappearance of Christ is more likely to happen before that...and even if weŽd build an airport, one never knows when thats going to open...