You have a very old set of dinnerware,probably over 100 years old. Established in 1898 GDA stand for Gerard-Dufraisseix and Abbot. I could not find your pattern on Rep.com. I cannot give an estimate. It depends on condition, beauty and how many pieces. Sugar, creamer tureen,bowls etc. If it has all the accesories it’s value could be over a thousand. does it have gold gilt etc. There is some complete set’s on e-bay to give an idea. You might want to check your library for more info and prices.