Works by Costis are found in museums and private collections in Greece, France, Belgium, Germany, etc., including:

• Fondation Electricite, Paris
• Espace Electra, Paris
• Electropolis, Mulhouse, France
• Bremish Autothek, Bremen, Germany
• Kanagawa Prefecture Gallery, Yokohama, Japan
• Györ Museum, "Oxygen" Foundation, Hungary
• Museum of International Contemporary Graphic Arts, Fredrikstad, Norway
• Musée du Petit Format, Couvin, Belgium
• Nicosia Historical Museum, Cyprus
• Baaz Art Foundation, Romania
• Skironio Museum, Athens
• Municipal Gallery, Athens
• Cycladic Gallery, Greece

etc.