ESP32 are small, low cost Bluetooth/WiFi boards that can be programmed using Arduino IDE. Shogunxam has a project, ESP32 BLETracker that detects Bluetooth LE devices and sends the information to a MQTT server.
The software provides a web interface that allows setting of the devices to be tracked, the scan period, MQTT parameters and viewing of the logs.
The project is open source on GitHub.
View Bluetooth Gateways