There's no context to the actual value of gil; even going by in-game vendor prices, values skew all over the place because the nature of an RPG with a linear progression of locations will inevitably ask you for more money as you progress, regardless of what's being sold or where. The podunk nowheresvilles in Shadowbringers ask more for the same sort of item than the capitalist hellscape that is Ul'Dah; not for an in-universe reason, but because later in the game they expect you to have more money lying around.

So, yeah. Suffice to say, we can't state a daily cost of living or something like that, because we do not have an operable metric to measure with.