I have one of the larger hobby mills a Industrial Hobbies mill and it is not to hard to be around +/- .002" for a smaller part of less than three inches working in aluminum.

I have also read all your post.

You just don't really understand how hard it is to work inside a .001" window.

The grinder idea might let you use a more standard mill and then do the grind.

You will still be closer to 15k if a used grinder is OK but you would have a chance that way.