You can buy Sensortags with sub-1GHz RF transmitters, which have a (theoretical) range of >500m, which should be enough for most applications to not require a mesh network at all. They also accurate clocks (with a crystal) to do time-rendezvous networking as well.

I've some intended for home monitoring-- they have "10 sensors including support for light, digital microphone, magnetic sensor, humidity, pressure, accelerometer, gyroscope, magnetometer, object temperature, and ambient temperature" for $30.