Coming from a machining background I can tell you that something more accurate than a drill press is required. Plus you had better be able to read a print working from an abstract zero.
Can you say coordinate geometry?
I have seen receivers that were 80 percent finished that were finish machined by accomplished machinists. They turned out decent but with only manual machines it involved a good bit of work.
My time on a machine makes the additional cost of a complete lower vs 80 percent seem cheap.(To me anyway)