… and having a property that fully encloses the entire previous example property boundary to a height of 10 meters, with full floor covering for 3 floors plus the roof all with rebar, that's only adding about $209k to the previous number: https://www.wolframalpha.com/input?i=%28%28800+*+4+%2B+%2810...
So, even with the largest possible structure fitting the same envelope, and the expensive end of the range for rebar, nowhere near the sale price of the property. Reducing this to the scale of the actual building that was there, nearly halves the cost of the rebar from 5% to 3% of the sale price, and the concrete (assuming 50cm thick walls and floors) in the range of 96-180k or 2.5-4.7% of the sale price.
It's *everything else* besides materials that makes houses expensive.
Given the low prices of adding reinforcement, the lesson from the Romans about getting by without reinforcement in concrete is more of an interesting side-note rather than a core point: https://en.wikipedia.org/wiki/Roman_concrete
Metal shutters is also uncommon, it's usually PVC.
What country you live in ?
Concrete is cheap but the steel used to reinforce it are not and concrete not reinforced is worth nothing so I don't know about your estimate.