[kbutler]

"Altogether the Delta Works cost nearly 5 billion Euros." http://www.deltawerken.com/The-Delta-Works/1524.html

"The South Holland coast region is home to approximately 4 million people who live below normal sea level" https://www.ice.org.uk/what-is-civil-engineering/what-do-civ...

Roughly 1300 Euros per person protected. How much would it cost to move those people? And what is the total value of the real estate where they live/work/farm?

So yes, "Building sea walls is a trivial cost compared to moving (and giving up the real estate to the sea)."