So I've been messing around trying to make the cheapest possible home automation setup, and with help from my friend Abhi, here's what we came up with, including all the equipment, connections and code:

https://www.homesecuritylist.com/diy-home-automation-system-under-40-dollars/

Here's everything we used:

• 1x NodeMCU board (Price: $8)
• 1x Relay (Price: $6)
• 1x TMP36 Temperature sensor (Price: $ 2)
• 1x HC-SR501 PIR Sensor (Price: $2)
• 9-12V 1.0A DC Adapter (Price: $6)
• 3.3V/5V power supply module (Price: $6)
• 1x Breadboard (Price: $5)
• Jumper/electric wires (Price: $1)
• Bidirectional logic-level shifter (Price: $1)
• 1x bulb/appliance that you want to control (Price: $2)

We also did one with Raspberry Pi and Alexa which is really fun.