Manufacture metal pieces

[JAZZCNC]

Nearly impossible to answer because it depends on the part and the accuracy you are aiming for and how good a job you make of the first attempt.

For a milling machine then you'll want fairly good accuracy and you may find it cheaper and less hassle to have the main important parts made for you and important surfaces machined flat and parallel etc.

This will save you time and money long term as you will only do it one time rather than spending weeks or months making failed attempts as you chase accuracy.
Often trying to save money in the wrong places costs money long-term and becomes a false economy.