The antonyms for the word "most unextravagant" would be extravagant, lavish, wasteful, exorbitant, and prodigal. These words refer to an excessive or extreme display of wealth, luxury, or spending. An extravagant person is one who spends money frivolously on things that they do not need or cannot afford. On the other hand, an unextravagant person is modest, frugal, and mindful of their spending. While being frugal is a desirable trait, being extravagant can lead to financial instability and debt. Therefore, it is important to strike a balance between the two and live within your means while enjoying life's pleasures in a responsible manner.