For those who don't like the sound of taking all the buses from Heraklion Airport to Plakias, but want to save some of the money, there is "in-between" solution.
1. Take a taxi from the airport to the bus station in Heraklion (make sure you ask for the bus station for Rethmynon, as there are 3 stations). It will take about 15 mins. Make sure you find out the official fare, as this is the type of journey where you are very likely to get fleeced. It should be about €5 I would have thought.
2. Take the bus to Rethymnon. These run at least every hour and often every half hour, so you won't have too long to wait. Moving cases from where the taxi driver has put them onto the bus will be 3 or 4 yards.
3. At Rethymon bus station you have a decision to make. Buses to Plakias aren't very frequent, so you either take one if there is one or get another taxi to Plakias. The bus conductors will lift your luggage out of and into the bus, and the bus station is small, so you won't have any distance to walk. The bus jouriney to Plakias is 40 minutes. About 7 or 8 years ago I shared a taxi with a couple and it was 4000 drs (€12) - this was after the last bus had gone.
Greecemad.