The sea route is only 453 km and took only about a week, but it cost about 65 denarii each way per person in the first century. It therefore cost about 390 denarii to send the three men to Ephesus.
Now, what does all this tell us about the purpose of the journey of Stephanas, Fortunatus and Achaicus to Ephesus? It is normally assumed that they visited Ephesus to deliver the Corinthians' letter, at the request of the church. But if this were the case it is surprising that three people were sent. Why would the Corinthians not have sent just one letter carrier by sea, costing just 130 denarii for the round trip? Why expose three people to the dangers of shipwreck when only one was needed? People did not make unnecessary journeys and the group of three men demands an explanation. No explanation has been given before, as far as I know.
All is clear when we accept that Paul had honoured Gaius, by giving him the name "Stephanas", as I argued here. The church meetings were held in the house of Gaius-Stephanas (Rom 16:23). It was therefore the role of Stephanas and his household to control the proceedings, but the meetings had become disorderly (1 Cor 11-14) because the church members did not show enough respect for their hosts. Stephanas and two members of his household (Fortunatus and Achaicus) therefore travelled to Ephesus to report the problems to Paul and solicit his support, which he gave in 1 Cor 16:15-18. Fortunatus and Achaicus accompanied Stephanas because they shared with him the responsibility of hosting the church and they too needed Paul's endorsement if they were to be able to control the unruly congregation.
The church as a whole did not initiate the visit of the three men to Ephesus. They went on their own initiative and the church merely took the opportunity to send a letter with them.