A good deal, but not quite a steal. I got a NIB pre-B CZ75 about a year ago, for $400. Original box, two matching serial numbered 15rd mags. That was a STEAL.
I'd try to bargain him down a bit, but $425 is fair. Beautiful gun, BTW - I love the spur hammer on the old ones, much better looking than the ring hammer on the newer CZs.