We know that it is very costly to hire a Faceless Man, especially if the victim is an important person. In the previous books it was said that to send a FM after Daenerys, when she was still a girl and not even a khaleesi, would have been the same as to hire an army. It was also mentioned that one dragon egg is enough to hire a fleet of ships.
Balon was the lord of the Iron islands and at war for the position of the king. So a dragon egg could just about meet the price for his head.
The last we heard of Jaqen H'Ghar, he was infiltrating the Citadel. And Tyrion has said that the only surviving copy of the book "The Death of the Dragons" was supposedly hidden away in a locked vault beneath the Citadel. It is named "The Death of the Dragons", but it can be generally about dragons including information how to hatch them.
I admit not knowing how exactly would the FM plan to use a dragon that use being relevant to the plot.
EDIT: redriver wants it to be known that he thinks he came up with this theory (and I stole it).
Edited by A Free Shadow, 23 February 2012 - 04:03 PM.