This Wi-Fi-area temperature sensing & reporting project uses Wemos D1 mini boards, I2C temperature sensors, 7-segment displays, neopixels, buttons, and project boxes. Tasmota is used on sensor boxes, MicroPython on display boxes, and the Mosquitto MQTT server on hardware of your choice, e.g. a Raspberry Pi.

The BOM for each sensor/display box is approximately $8 (from Amazon.com), not including 5V/USB power adapters or cables. Any number of sensor & display boxes may be mixed-and-matched, with display box buttons controlling temp/humidity display and sensor group display. This specific project is configured for 4 sensor boxes in 2 indoor/outdoor groups and one display box.

Using Tasmota on sensor boxes allows them to be easily accessed from Home Assistant and, from there, smartphone apps plus any device with a local network connection & a web browser.