More subsidy than the existing sleeper shouldn’t be a surprise. The question is how much.
Even with cheap-as-chips leasing on the rolling stock, I can’t see how such an operation would cost less than £10m a year.
Of those 30,000 passengers, it’s reasonable to assume that many of them would have travelled by day train, but find the night service more convenient. So that isn’t new revenue (except for the premium of a berth). For the sake of making the maths simple, let’s say that 20,000 people are new to rail.
That would be £500 cost per passenger. Given that an anytime single from Wick to Glasgow is £71, and Inverness to Glasgow is £45, with many cheaper advance options, it’s going to be difficult to price a one way trip lower than an average of £100.
That means subsidy of £400+ per passenger. It would be cheaper to get each one a chauffeur driven limo.