Yeah seriously. Just the land for a regular house lot can easily be over a million dollars in the area, and 1 acre can hold like six of those. So five acres...like thirty million dollars? Unless there's some weird situation I've never heard of.

5 acres in area where minimum lot is 5 acres is much cheaper than in area where minimum is 5k sq ft. In most areas you can’t subdivide lot - that’s the reason houses in Atherton on huge lots are so cheap (relatively).

The land is what you're generally paying for in any real estate deal. It doesn't cost millions to build these houses, but the land is valued as such because it's finite.