Hondos centers are all around Athens. They are sort of like pharmacies/clothing/luggage/cosmetic stores. They have almost everything. They are cheap too, so if you are looking for something that falls under the categories I mentioned, you are sure to find it at a decent price.
What to buy: anything
What to pay: Depends on what you buy, but I would say Hondos Centers are generally low priced.
"Hondos Center" is a company which was created by Hondos brothers in 1967, nowadays many "Hondos Centers" can be found in cities all over Greece. The superstore in Omonia is a big one in Athens. (The biggest shopping centre in Athens is "The Mall" in Marousi, with about 200 shops in it. It was founded in November 2005.)
There are different departments at its floors, the last one houses a nice self service cafe-restaurant, which has a perfect view to the Acropolis!