"It is the prize for being a good man."
Translation:É o prêmio por ser um bom homem.
In cases like this, you can see "para" as destination and "por" as cause.
É o preço por ser um bom homem (because you are a good man, you have to pay some price in consequence)
É o preço para ser um bom homem (you must pay in order to becomea good man -- I know it's quite nonsense in this good man case, but other cases would make sense)
I feel like I should know this already, but why is the infinitive 'ser' used instead of 'sido'?
general rule - Eng: preposition + gerund -> Port: preposition + infinitive.