I don't remember Springfield offering nickel plated P9's, and the add mentions a "custom" plating, so I'd assume it's post-factory.
General consensus on the Springfield P9 is, it was about the top of the line of the CZ-75 clones.
As in almost all of the clones of the CZ, the P9 was made by Tanfoglio in Italy and finished here in the states by Springfield.
These are very good quality guns, accurate, reliable, and durable.
Price-wise, that seems high.
I bought a P9 in the late 1980's at $280.00, factory-direct.