How much is a mass production aluminium road bike frame worth?
There is no specific way to calculate the worth of a frame when taken from a complete bicycle.  The market will tell you how much it wants to pay for such a frame, but the theoretical calculation of "The frame is worth the complete bike price minus the price of all other components'" is wrong.  Firstly it's wrong because it ignores assembly and value-add pricing.  Secondly it's wrong because it ignores the steep discount you get when buying a complete bike.

Imagine asking how much the chassis of a Ford Explorer is worth.  If you try to buy all the other parts separately, the total will be more than double what a complete vehicle would cost.  Bikes are a bit like that.