Exactly this.I don't think you can come out with price quotes as a feasibility study of such a line to the proposed *new terminal* hasn't yet been carried out.
Councillor Andrew Carter (Conservative) at a recent Leeds City Council meeting was quoted for saying additional money for infrastructure projects are likely to be made available following the overwhelming support the government had for their Brexit handling. Not something I personally endorsed but lets see if additional money is made available.
The question needs to be reasked and experts (not Internet forum desktop experts) need to re evaluate...
The location of a direct spur would now be completely different, shorter and over different topography.
Also it is somewhat flawed to value a direct rail station based on user numbers alone... What if the convenience of a direct rail link encourages a foreign firm to locate in Leeds rather than other northern cities? That value wouldn't be captured by passenger numbers... But would be worth so much to the local economy.