How would I set up a free dedicated server? All the ones I've found cost money.
You'd need your own server machine.
Theoretically you can host one from your own computer, but then your computer would have more than two thirds of it's system resources used up by the server, rendering it almost useless to you, and the server itself wouldn't perform anywhere near good enough.
So, unless you have your own server system locked away somewhere, I'd advise renting, or not bothering.
I don't know how, and I don't know why, but this is totally Sheep's fault.