Unfortunately, there is no simple answer to that, because governments have a sometimes terrifying way of obscuring costs, especially for capital investments. If you were looking for an example, I think the Paris-Lyons line, if you could get the numbers, is the one you would go to. I think you would look at a couple of routes in Sweden where I think there are some decent numbers.
The general answer is that you're going to be disappointed. The other general answer is that you're going to find that usually they have been subsidized, and sometimes quite heavily.
If I could comment on the fragility, I absolutely agree with you. However, there is one 800-pound elephant in the corner, and it's oil prices.