Hi, I have just returned from Plakias, and can confirm the taxis as 100 euros from the airport, but only 80 euros from Plakias, so if you can pre book a taxi from Plakias you should save a little.
I have not tried the Alianthos Gardens, but a couple I met on the return transfer found it somewhat noisy as many people arrive/leave at odd hours in the middle o the night, plus, of course, it is more expensive being half board, thus reducing the opportunities to sample all of the great tavernas etc. in Plakias.
Assuming Googlr earth is up to date, there are not many places with a pool. I stayed again at Costas Chrysoulla, and found it ideal for doing exactly what you say you want to do. It is basic, but clean, and very typically Greek, and has air conditioning if you want it (5€ a day). I would certainly be happy going there again, and I will - can't wait to be back in Plak again.
The return transfer with Olympic was AWFUL, and I am about to make a major complaint to Olympic about the time/queues, and nearly missing the flight. Nuf said, 80€ is a bargain!