Create a new wireless protocol for industrial
One of the disadvantage associated with zigbee modules for communication is the high cost. Moreover Zigbee is intended for short range. 

Radio links are the cheapest and long range solutions. NRF24L01 is one such radio link solution.
NRF24L01 comprises 2Mbps RF transceiver IC for the 2.4GHz ISM (Industrial, Scientific and Medical) band. Extremely low power and reliable. I have once worked with these modules and result was good. I recommend you to search for the latest version.