Airfare to Hungary for the summer?

We are planning to take a family vacation next summer to Hungary, for the lenght of 3 or 3 and a half weeks in July. Does anyone know when is the best time to buy those tickets, like how far in advance? And where can I get the best deals? Anyone knows a website or a good agent? We are a family of four: 2 adults, 2 children age 17 and 11. Thanks Niki