In Santorini you will find branches of the bigger Greek banks, to cover your needs.

In Fira, you'll find Agrotiki, Alpha, Ethniki, Emporiki, Eurobank. In the Fira-Pyrgos Road you will find Piraeus and Alpha Bank, while during the summer season yyou will also find branches of Alpha Bank in Oia and Ethniki in Kamari.

ATM machines can be found almost everywhere.

Some of the banks from which you can get served are:

1) Agrotiki Bank (Fira) +30 22860 22738, 22103
2) Alpha Bank (Fira) +30 22860 23800
3) Emporiki Bank (Fira) +30 22860 21021
4) National Bank (Fira) +30 22860 21051, 21054
5) Piraeus Bank (Karterados) +30 22860 21000