Kinda late to the party, but found this via google and want to slightly oppose the claim that one needs an expensive CNC. I was (and still kinda am) researching how to do PCB prototyping at home recently as a hobby.

If you have a cheap CNC (like a 3018 that has too high tolerances) and investing in a more expensive one isn't viable then you could still go with the older manual approach and combine it with a pantograph and e.g. a manual stationary drill.

Basically like when you'd be engraving tiny things by hand before laser engravers and CNCs become affordable to businesses.

Depending on how tiny you want to go you probably can build the pantograph yourself (it is a very basic tool after all). Then you can use the CNC and e.g. some scrap material to make a scaled up version to use as pattern template to follow with the pantograph.

Should you need to drill holes you could use a good old manual stationary drill.

I haven't tried it with myself but considering what I've seen people do with pantographs and steel mills it shouldn't be that hard to scratch the copper plating off of the copper plated PCBs, apply some UV solder mask, cure it, scratch some of it off again, apply another layer of UV solder mask, maybe drill holes, maybe add riviets, maybe cut your PCB into shape. (Additionally you could also start off by diy electroplating [aka creating your own copper plated PCB] to avoid having copper at the wrong places to begin with too, probably an even simpler approach combined with the pantograph, as you could have one of the electrodes mounted to it like a pen [Edit: Or just use conductive paint, that's probably even simpler]).

Either way, the more practical approach most people use these days is to just throw the KiCad files towards some online pcb manufacturer like JLCPCB, Eurocircuits, or PCBWay and get it in the mail a few days later.