The past tense of spend money as if it were going out of style is spent money as if it were going out of style.

The third-person singular simple present indicative form of spend money as if it were going out of style is spends money as if it were going out of style.

The present participle of spend money as if it were going out of style is spending money as if it were going out of style.

The past participle of spend money as if it were going out of style is spent money as if it were going out of style.