Go through your results for flights to Preveza/Lefkas in Greece with Netflights. The most popular airlines for this route are British Airways, Austrian Airlines & EasyJet, with British Airways claiming the top spot.
If these flights are too expensive, try searching for a different time of year. So if your dates are flexible, consider looking at different times of year.
So, if the flights to Preveza/Lefkas don't work for you, you could always try searching for flights to other airports in Greece.
For even more options, check what other airports you could fly to Preveza/Lefkas from. You might be able to make a saving by going from a different airport or city. The most popular airports with direct flights to Preveza/Lefkas are London Heathrow (LHR) & London Gatwick (LGW).