The seller appears to be very proud of his offering. That is a steep starting price...at least in my mind. These don't come to market often, but I sure don't see it commanding this price.
As for finding extra magazines, this should be the same magazine that the PT-940 .40SW uses and be fairly easy to find. If I recall the 940 is a 10 round magazine, I could go look in my storage locker, but I'm too lazy at the moment to do so.