Domestic SKU-ATH can be had for 17 euro through an OTA or 20 through the Aegean website. Of course the other way around will be higher due to the taxes departing from ATH.

One thing I've realised booking Aegean... is to wait for sales whenever possible. Make sure to book early for summer, and only during their 40% sales for winter. Especially when aiming to buy Flex fares that makes a huge difference on the total price.