Explanation:

- Extravagant: Characterized by spending too much, lavishness, or unnecessary excessiveness.

- Option 1: Deficient: Means lacking in some necessary quality or element. It doesn't directly relate to spending habits.

- Option 2: Resentful: Refers to feeling or expressing bitterness or indignation, not related to spending.

- Option 3: Wasteful: Describes using resources carelessly. This is a synonym, not an antonym, to extravagant.

- Option 4: Thrifty: Implies being careful with money, avoiding unnecessary expenditure, which is directly opposite to extravagant.

Your understanding aligns with the correct logic. The antonym of "extravagant" is indeed thrifty.