As any parent knows, toy train sets can get expensive. But $2 million? Robert Mercer, a top executive at Renaissance Technologies, has accused a custom model railroad designer of overcharging him by nearly that amount for an elaborate toy railroad installed in his home on Long Island, according to a complaint filed in Central Islip Federal Court. In court documents, Mercer claims that the correct amount for the labor and materials should be closer to $704,669, and that the bill was "wrongfully and fraudulently" padded. The model reportedly has museum-quality detail and is half the size of a basketball court.