You can get to Eski Foça from Izmir entirely via public transportation. It takes about an hour and 20 minutes to get there.
To get there, take the IZBAN metro line in the Aliaği direction (NOTE: watch the trains that come in and do not get on a metro that says "Menemen" - you need to go one stop further than Menemen). Get off at the Hatundere stop and exit the metro, the 744 bus to Foça will normally be waiting right in front of the platform. The combined fare for the metro and bus is 4TL one way.
There is also a dolmuş that runs directly from İzmir to Foça, but unfortunately I do not know the prices, times, or locations for this.
The bus/metro cost 4TL combined.
The public beach is free, and there a number of other beach clubs in the area
There are also a variety of boat tours that leave from the area, but I do not have pricing information on these.