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.
As far as the laws of mathematics refer to reality, they are not
certain, and as far as they are certain, they do not refer to reality.
— Albert Einstein