BTW... It is also worth going to the First Choice site as they sometimes do better deals/have different availability on the same flight. ( I constantly monitor the 2 sites for the flight to Antigua)
you could also try www.satellitetravel.co.uk and Sailing Holidays will also sell you seats on their flights to Preveza -- I think they show availability on their website also.
just a thought , we often go via Corfu to preveza , its very easy and often cheaper flight will compensate for taxi fare .igoumonitsa to prevza 70 eruo in taxi -1.5 hours trip or 10 euro on local bus -3 hours to preveza from igoumonitsa .lots of ferries every day from corfu -8 euro .Its a good alternative and very enjoyable trip .Doing it this Saturday when we go for three weeks ,back home from Preveza though .Both flights from sailing holidays