Just got an ad from Bangood and it has a P3 battery for $100. Of course it's a knock-off but it is probably worth a look see..
4500mAh 15.2V 4S Intelligent Battery For DJI Phantom 3 Professional Advance Standard Versions
4500mAh 15.2V 4S Intelligent Battery For DJI Phantom 3 Professional Advance Standard Versions