Brother I know that Mumbai-Delhi passengers can easily pay this much but I'm just giving a justification. 3 AC BCT-NDLS ticket by BCT Rajdhani costs approx 1800 rs. Whereas railway is charging 3900 for this train in spite of these many berths still available.. I think RB should start charging dynamically only once train has less than 200 or 150 berths available.
However this train is a great help for any last minute passenger in this premium route.