You can easily get accuracy of much less than a mm. I would suggest a cnc'ed Taig mill as a good option. It is reasonably priced and, with a well selected controller/motor package, can be up and running in a couple of hours. The travels are roughly 12x6x6 so it falls a bit short in the Y direction. However you can probably work around that quite easily.
You want to buy one with a Gecko G540 based controller. A couple of dealers who offer those are;
soigeneris (you will have to google them)
I bought from deepgroove1 before the G540 came out and have since upgraded to the Gecko. I have ordered parts and accessories from Soigneris and have been pleased with the service. I think Soigeneris' controller is a bit nicer but you pay a bit more.