D&D 5E - The Intent of the Forbiddance Spell

A is correct by the way the rules are written - but that doesn't mean it is "meh, who cares, it's 1,000 gp." because it isn't just 1,000 gp, it is 1,000 gp that you spent on a specific not all that common component, or a 1,000 gp quantity of rubies that you found and took the time to crush into dust (or maybe an even larger quantity of rubies you found and cut so that the 1,000 gp quantity of dust is a byproduct).

The monetary cost, combined with the stay in one place for a month cost, makes the spell's permanent version "woah, this is a significant investment."