The average fee for a TRX transaction in the blockchain depends on the amount of data being sent, the network congestion, and the type of token being used. For example, transactions involving SUN and BTT tokens tend to have higher fees than other types of transactions because of their higher data requirements. However, the exact fee for a transaction can be determined by using a service such as Tronlink, which provides real-time fee estimates for various types of transactions. Tronlink also provides estimated times for transactions to be completed, allowing users to plan their transactions accordingly.