Yankees catcher Jorge Posada is a free agent this winter, but is paying millions to expand his already spacious Upper East Side home. The Post's Braden Keil reports the $12 million-a-year Bronx Bomber and his wife, Laura, just paid $3.6 million for the three-bedroom apartment that became available next door to their four-bedroom condo on East 77th Street. "We built this place from scratch - it's exactly what we wanted," Posada said of the original 3,400-square-foot spread that he bought in 2003.