It wouldn't be worth the trouble. no valdría la pena. no valdrías la pena. no valdríamos la pena. no valdrían la pena.

No valdría la pena

Explanation:

The key here is te conjugation of the verb.

In spanish, it's common to omit the pronoun, because the conjugation of the verb is unique to every pronoun, so based on the conjugation, the pronoun can be determined.

No valdrías la pena: Valdrías is the conjugation of the verb Valer (to cost or to be worth) in 2nd person singular "Tú" (you), in the simple conditional tense. So it translates to "You wouldn't be worth the trouble".

No valdríamos la pena: Valdríamos is the conjugation of the verb Valer  (to cost or to be worth) in 2nd person plural "Nosotros" (we), in the simple conditional tense. So it translates to "We wouldn't be worth the trouble".

No valdrían la pena: Valdrían is the conjugation of the verb Valer  (to cost or to be worth) in 3nd person plural "Ellos" (They), in the simple conditional tense. So it translates to "They wouldn't be worth the trouble".

No valdría la pena is the correct option. Valdría is the conjugation of the verb Valer  (to cost or to be worth) in 3nd person singular "Él, Ella, Eso" (He, she, it) in the simple conditional tense. So it translates to "It wouldn't be worth the trouble".

yes you are correct