With a surface area of 181 sq. km * 1 meter thick = 181,000,000 cubic meters. I'm seeing numbers like $20/ton for sand and rocks and there's not quite 2 tons of sand / cubic meter, giving $7 billion in materials, or $100K/person or >50x the GDP.

Plus transport costs, which I can't even begin to estimate.

And that's mostly just to cover the estimated sea level rise since the 1950s. It doesn't handle 3 meter waves from the recent storm events.

And of course this doesn't change the decrease in rainfall.