Cheap Zigbee PIR sensor

I am developing own software which read PIR sensor (motion detection) data and start ip camera recording if needed.
What sensor is cheapest for that purpose?
I don’t know very much about zigbee, just some basic details.
I also need zigbee receiver to raspberry pi or some openwrt router. It might be first easiest to start from rapberry pi. There is at least two zigbee receivers for Raspberry pi, xbee and RaspBee. How I then know that this sensor suppor one of those? How to connect sensor to raspberry receiver? I will use C++ code, but some existing script or other programming language could be also useful.