ESP
ESP32
These $10 ESP32 modules from various aliexpress sellers (one example) have a SSD1306 128x64 white OLED display and a SX1278 LoRa radio module. They also include a LiPo battery charger and two buttons (one is wired to reset, so it isn't as useful). There is a slightly more expensive version with a blue OLED with a 900 Mhz radio.
It is programmable with the normal ESP32 Arduino IDE, using the board type ESP32 Dev Module and programmable over the /dev/ttyUSB0 port. On OSX and Windows you might need to install
a driver for the CP2102 USB to UART bridge from Silicon Labs.
Source and demos for using them are in github.com/osresearch/esp32-ttgo
ESP8266
The ESP8266 is the older version and not quite as powerful. They can run for several hours on a coin cell.