DIY wireless smart Temperature & Humidity sensor that can be added in Home Assistant can be very easy and cheap. Especially, if you have a complete guide like this one that will show you all the steps.
I will try my best to show you everything: what parts are needed, how much they cost, from where to buy them, how to connect them, how to configure them, how to install ESPHome and finally how to add your smart DIY Temperature & Humidity sensor to Home Assistant.
Hope that this is going to be useful for you!
WATCH HERE Cheap DIY Temperature & Humidity Sensor that works with ESPHome & Home Assistant - YouTube
READ HERE https://peyanski.com/diy-temperature-sensor-for-home-assistant/
Cheers,
Kiril