The antonym of frugal (someone who is careful with money) is spendthrift (someone who wastes money).

১. ‘Economical’ is a synonym of frugal, not an antonym.
২. ‘Extraordinary’ and ‘Authentic’ are unrelated to the context of monetary spending.
৩. A frugal person avoids waste, whereas a spendthrift spends recklessly.

অতিরিক্ত তথ্য: Frugality is often seen as a virtue, while being a spendthrift is seen as a vice.