Just bought a Dragino LDS02 door sensor that I want to use to notify me when we get mail at our “cluster” mailbox that’s about 300 meters away from our house. I live in Divide, Colorado (VERY rural.) I noticed that there were two Helium hotspots 3km west of us, so I was hoping my sensor would reach them. I set up my device in the Helium console and connected the batteries, but no joy. 
So it looks like I need to set up my own hotspot. Being so far out in the sticks, I don’t see much point in trying to “optimize for my-ning.” All I need is something that my sensor can reach purely for my own use.
What’s the CHEAPEST I can get with enough range for my sensor to reach?