I'm currently designing and working out moulds etc to build small Fixed gantry Epoxy Granite based machine. It will have profiled linear rails and use Closed loop stepper system using preloaded double-nut ball-screws.
The Epoxy granite structure will minimise vibrations and resonance and coupled with linear rails will make for very high quality surface finish. The preloaded double nut will make for near zero backlash and coupled with Closed loop steppers will make it very accurate. Will most likely have 2.2Kw spindle on it which will just about match the machine accuracy.

Reason for telling this is because I'm sure it will cost less than any small converted CNC mill and will hold much better tolerances and be more suited to your type of work due to spindle. You'll need to spend at least £10k to get off the shelf machine that will hold tolerances anywhere near what machine built like this will hold.

Even a fixed gantry steel framed machine filled with sand or Resin/aggregate mix with same double nut and closed loop steppers and WC spindle will blow the small Chinese milling machines away and be cheaper to build.

MY ADVISE IS BUILD BUILD BUILD has you'll only be disappointed or limited with Cheap Chinese mill conversion.!!