Aldaberto Mondesi signed with the Royals for 2 million.
Humberto Arteaga signed for 1.1 million.
Orlando Calixte signed for 1 million.
There are a lot of factors in play here. Mondesi has the benefit of exposure from the DPL, his father's experience in the majors, and IFA bonuses have been on the increase. But the Royals paid a hefty price for Mondesi, especially relative to Arteaga, who was just as well thought of (Baseball America predicted Mondesi would get the 12th highest signing bonus in 2011 and Arteaga would get the 11th highest bonus in 2010). The LA shortstop crop wasn't particularly good this year by most accounts too. Even more, the Yankees supposedly tried to get in on Mondesi.
Perhaps the biggest difference between the three men above: Mondesi was born in the United States while his father played for the Dodgers. Mondesi's identity is a near certainty (unless the real Aldaberto Mondesi is somewhere else).
What is the true value of age-certainty? It would seem that the value would be at least the amount of an insurance policy to take out on the signing bonus you would give to another IFA signee. On top of that, there are your costs of development which might be useless if a kid is actually 3 years older and won't ever amount to anything. Even more, does it reflect the opportunity cost of devoting instruction and playing time to a kid who isn't a real prospect?