Opal benefits Lower fares: Opal card fares are cheaper than Opal single trip tickets and Opal single bus tickets. Capped fares – No matter how much you travel with Opal, you never pay more than your daily, Weekly or Sunday travel caps. The card is free when you load a minimum amount onto it. The minimum cost is $10 for adult cards, $5 for child cards (other types such as seniors and students cards must be ordered). The only exception to this is if you buy your card at the airport train stations where the minimum top-up is $35.