Does it cost something to transfer Avios between Finnair Plus and The British Airways Club?

No, it doesn’t. Transferring Avios between your Finnair Plus and the Club accounts is free of charge. Avios are worth the same in both programs: 1 Avios in Finnair Plus equals 1 Avios in the Club. You can also transfer your Avios between your accounts as often as you wish. Read more about transferring Avios.