Earlier quoted context omitted.
> There is nothing off the shelf, even if some other subway gave them all the design (unlikely), it would still be hundreds of thousands of dollars per train to make it fit the New York trains. What? Alstom, Ansaldo STS, Bombardier, Siemens, and Thales all have off-the-shelf designs that they will happily sell. And I've probably forgotten some here. I realise none of these are American companies, and "Buy American" i…
That's the com system, but there are fully automated off-the-shelf systems (com, rolling stock, …). Two examples are Siemens's VAL (Lille, Taipei's Brown, Seoul's U-line, VAL tech has also been used in Lyon's D and Paris's 14 and 1) and Hitachi's AnsaldoBreda Driverless (Copenhagen, Taipei's Yellow, Milan 5, …). The latter is very popular and getting deployed in several places right now: Honolulu, Thessaloniki, Lima…
To nitpick, this is actually Hitachi (the ex-AnsaldoBreda part) and Ansaldo STS (which Hitachi only bought 40% of, and became its own company when Hitachi bought AnsaldoBreda).
Depending on rolling stock and space for equipment, replacing the rolling stock when replacing the signalling equipment might not be required (see, for example, the the London Underground 1995 Stock on the Northern Line).