The most “apples to apples” comparison that comes to mind for “structural” (eg levees, etc) and “non structural” (eg relocations) flood risk management is Minot, ND vs Fargo, ND. This is fluvial (riverine) flooding rather than coastal, so the math is different wrt economic considerations, but the math isn’t too much different.

Like others have said though, the politics of relocations are extremely thorny, leading to inflation of otherwise cost-effective methods. Especially when there’s minimal investment in education or other methods of helping communities make informed decisions about zoning (besides what their favorite news radio hosts say)

Examples: Minot buyout documentation

https://www.adaptationclearinghouse.org/resources/minot-north-dakota-floodplain-buyouts-and-affordable-resilient-housing-e-buy-in-e-program.html

https://www.minotnd.gov/DocumentCenter/View/8243/Residential-Tenant-Relocation-Assistance-Plan

Fargo-Moorhead Diversion https://fmdiversion.gov/

https://www.swc.nd.gov/info_edu/water_development_plan/wdp/large_projects/fargo_moorhead_area_diversion_project.pdf