Amazon.com: HiLetgo ESP32 SX1262 LoRa Kit 863-928MHz Bluetooth 4.2+WiFi+LoRa LoRaWAN Wireless Communication Development Board with 0.49" OLED Display 64M Bits Flash Works with Arduino IDE Type C : Electronics
Wireless communication between two Arduinos using inexpensive RF modules | Embedded Lab
VirtualWire Library, for very cheap wireless communication
Interfacing nRF24L01 With Arduino UNO-Wireless Communication