Micro Center is selling the Raspberry Pi Zero for 99¢ as a loss leader. I bought one, then spent another few bucks for a boot disk and a USB-to-Ethernet adapter and a minimal case. Total investment: about $15.
I’m using it as a Pi-Hole machine.
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.
— George Bernard Shaw