So 900 euro per month is expensive for a house like the one asked for here for the months of july and august? I would say it's cheap per week for those months and at this price well below prices quoted on the internet!
I was talking about long term rental (and that generally means at least a year in the Greek market). Of course you can get A LOT more per week in the high season. You'll also be breaking the law unless you have an EOT license. I'll let others tell you what the consequences of getting caught would be as I am not familiar with this but I believe that it's not pretty.