Varkiza its quite far and taxi quite expensive. You can get to lavrio port with frequent bus routes from airport, 40 minutes,, 5 euros per passenger estimated. Taxi estimated 30-40. There u can have nice food just behind the fresh fish market. If have some time u can take taxi to Poseidon Temple at Sounio, 15 minutes from lavrio The Temple is built on the rock cliff facing the aegean sea.
You can also take MRT just cross the airport exit to Syntagma Square, 40 minutes for pics and plenty food/drink choices.