By metro + KTEL bus
My apartment has ideal location to access Rafina port and Lavrio port. From Holargos metro station you just have to go to Nomismatokopio metro station (just 1 stop), and from there you can take KTEL Attikis bus (the orange-white buses) to the port.
There are metro trains every 3-6 minutes. Trip duration is just 1 minute. Tickets cost 1.20€ and are valid for 90 minutes. More information about first and last trains here. More information about tickets here. Alternatively you can just walk 17 minutes
At Nomimsmatokopio is the but stop where KTEL Attikis buses depart to the Rafina port and to Lavrio port. Travel time to the port is 45-50 minutes. You issue tickets on the bus with cash. It costs 2.40€. More information about KTEL bus tickets here for Rafina and here for Lavrio.
Read more: My apartment is located in a strategic location to access Airport, Port, Bus and Railway stations