And now it’s happening in midtown. First it was the 9/11 memorial that got too expensive and had to be reconsidered. Then it was the MTA’s Fulton Street transit hub that to be redesigned to cut costs: Its soaring glass dome has become less soaring and entirely stainless steel. Then, last week, it turned out that Santo Calatrava’s World Trade Center PATH station — for a long time, the only ground-zero building that seemed to be getting anywhere — was a billion dollars over budget and would also have to be scaled down. Now today’s Times brings word that, oh, yeah, the planned extension of the 7 train is likely to come hundreds of millions of dollars, or even maybe a billion dollars, over budget, and the MTA won’t grant any contracts to start work on the project until the city comes up with a new deal to finance the thing. And so it becomes clearer and clearer why it’s taken 80 years to build the Second Avenue line.