It's the law of diminishing returns... that last 20% or less in quality/finish/feature set, etc, often cost 80% or even more to get. Often times its more like that last 2- 5% costs 100% more.
It is not just parts, fit, appearance. At a point right between top of the line all bar stick steel parts and a custom hand fit pistol is a place where the difference is in the skill of the gunsmith. This is where the real value / cost comes in. You get what you pay for when your 1911 is built by someone with 25 years of experience.