Does anyone know how to get their hands on a Pi at the moment? Even Pi 3s are going for $100+ on eBay. rpilocator shows everything always out of stock.
I do not know about a Pi, but you can run Pi-hole on old(cheap) hardware with linux. You do not need a Raspberry Pi. I have Ubuntu Server running it. It is quite simple(two commands?) and there are plenty of tutorials out there. Odroid is a good alternative to Pi that can run Pi-hole.
Be aware that that will consume substantially more power than a pi. Even my old MacBook seems to consume about 6W idle with the screen off compared to 1W for my cubieboard (~pi 1 equivalent). A PC is probably closer to 10-30W.
