Haven´t been in Haris, but for example Maria&Manolis, Christos or Kima -hotel at the bebble beach are good and Pavlos Studios outside the village two kjlometers to the Anidri beach. I think every hotel we have been, can rent rooms for one day or more and we have been there nearly 20 weeks during last ten years.
And if you go at low season, you don´t have to make a reservation, there are plenty of rooms. Go to Skala in the port and take a beer or frappe and ask, where can I go for few days. They know everyone there.