$400. They're saying it's a P1.
For $400 bucks, if it's in decent condition, isn't a bad price. They're kind of interesting. It's the first pistol design which was DA/SA, meaning it could be fired in either double action of single action mode.
It was also the first widely manufactured semi-auto design to have a decocking mechanism which meant you could carry it safely with a round in the chamber and the hammer down.
To fire the user simply had to draw and pull the trigger just like a double action revolver. They're chambered for the 9MM cartridge.
Why are you considering the purchase of this particular weapon?