12v psu, approx £30
12v (good quality) pir, approx £8.
NodeMCU approx £2.
Roll of wire approx £20.
I've done the whole house this way. A fair bit of time/effort though. Single 12V psu with a handful of cheap 12v-5v usb modules mounted in backboxes with the NodeMCU's. Some connected to temp sensors plus pirs, door sensors etc and the odd relay.
Cost savings compared to standard smart tech is immense.
/ personal preference
