My agent called me telling me State Farm said to rebuild my 100k something duplex, it would cost 500k.

We had some problems with our driveway and need to rebuild it. 

+1 I pay about $300/mo for insurance on similar rebuild cost with very high deductibles and low coverages in Cape Coral without flood insurance.

While insurance might rebuild your property, the bigger issue is the loss of jobs, local businesses, and essential amenities.

After continuously rebuilding inventories from the fall of 2021 through the fall of 2022, retailers and wholesalers are pausing further inventory accumulation out of caution over the economic outlook causing U.S. imports to decline from record highs.

Property was purchased to avoid a hefty tax bill in 2016 and I took my time rebuilding it to sharpen my construction & carpenter skills.

It could cost millions to rehab/rebuild.

I had to brace and rebuild part of the upstairs balcony floor before I waterproofed and tiled it.

Chauncey,The Increase in your Homeowners or Dwelling Fire Coverage is likely due to an increase in the Replacement (rebuilding) Cost that the Insurance company requires. 

In terms of replacement cost, you will need to consider the cost to re-build (vs. market value).