Little Machine Shop sells a CNC mill for 5K. They usually invite potential customers to see the mill in action so they can have a good idea of the mill's performance, limits an so on. Sherline sells small CNC machines and I once saw a CNC conversion kit for a Proxxon mini mill that included automatic tool change ... lovely little thing.
But as mentioned in other threads you should first define what do you want to do with a PCNC so you can define how big or small your machine should be. Do you plan to build small steam engines? Or a 3 1/2 gauge locomotive?
Caveat emptor (buyer beware), remember that once you have purchased your CNC you may need an additional 5K for tooling, accessories, measurement and layout instruments ...