You understand correctly, yes! I would add that "extravagance" means more than "unusual". An extravagant lifestyle or behavior is usually very costly. Famous investor Warren Buffett's greatest extravagance was to buy a private jet to travel around the country. You could also say that you spent an extravagant night in New York City: you went to a Broadway show in a limousine, ate in an expensive restaurant, and stayed at the Waldorf-Astoria! Someone's greatest extravagance might also be an expensive car, drinking one glass of a rare Cognac every night.

extravagance mean over money wasteg