I wouldn't fixate on the cost of the construction in open country. It's the terminal costs that are prohibitive.
The railways have a virtual monopoly on the corridors in urban areas where land costs can be very high.
A good example is Edmonton-Calgary, or Saskatoon-Regina-Moose Jaw, or Halifax/Saint John. Even if a disused rail line can be rehabilitated, good luck getting access for the last few miles to a proper terminal location. I'm not a fan of placing stations in the suburbs.... and if the plan requires connecting to smaller communities to add ridership (eg Edmonton-Lethbridge, Halifax-Fredericton, Regina-Prince Albert) - then there will have to be a passage from one side of town to the other.
Whatever passenger trackage and infrastructure might have existed, it's gone now. Service and connecting tracks are torn up as well, so needed trackage may have a working freight train sitting on it. The railways won't be paying to put it back, or moving their trains out of the way on the existing track.. And nobody will be expropriating the land to add a new corridor.
This is even a concern for HFR. For the lighter-ridership corridors that one might suggest, it's crippling.
- Paul