Best wireless network architecture

[intruder195]

Hi All..
I have to design a wireless network as follows:
I have 1000 sensors.. Each sensor, on detecting something has to post the "detected info" on the cloud.
The distance between two sensors is 2.5 meters..
What is the best, simplest, no packet loss, cost effective , congestion free, interference free wireless network..?
Xbee is bit costly and needs a co-ordinator additionally..
WiFi .... May/May not get the signal for such long range ..(If 50 sensors are in series)
Lora... 1000 LoRas...?????


Any Hopping network?