I'm a total newbie to cnc milling.

People I heard weren't to enthusiastic about these machines for PCB prototyping.
There are many problems with the machines for this purpose according to them.

I'm an electronics hobbyist that hasn't much time for him hobby but when I start I want to have something at the end of the day :-)
My guess was that an milling machine would do a much better job than the chemical way of making PCB's.

I found out that zero backlash is very important, the power of the spindle and so on.
In my simple brains it's very simple: buy a machine, unbox it and start making the perfect PCB's from PCB design software.
But things are different in the real world.

What do I need to know to get as close as possible to my ideal way of making a PCB from scratch.
It seems that a PCB design can be exported from Eagle PCB software to (Mach3?) software to be milled in the machine.

What could be my expectations after buying a machine and start cutting?
What width of PCB traces I can expect from a cheap machine?
Is the price of the machine an indication for what quality of PCB I can expect?

Where can I read more about this?
Is there an Ebay seller that has a descent machine for a reasonable price?
All info is welcome!