Cheap wireless module for M2M communication
I'm designing a wireless device now and have looked through different options. Now  i'm deciding what to use between two choices:


Sub 1GHz radio chips or modules such as RFM12B or Silabs Si4455. They are very cheap and can give a good range of about kilometer. But if your base station is, say, 2km away from one of wireless devices — it will be no link because this modules don't give you a mesh. You have to code it by yourself.
ZigBee modules or SoC like Atmega128RFA1 can have a higher price but give you ready to use MAC addressing and Mesh network. Mesh netwok allows you to connect two devices, which have no direct link, via third device in between of them. This allows you to build large-area wireless netwoks. Also ZigBee is known for very small power consumption.