I seem to remember a quote of £2 billion for the accident from the insurance companies being bandied about. I was surprised by how high this number was, but have no idea how accurate it was, as the quote was from the first day of the accident, not a considered quote after all the details had been found out. I suspect £2 billion would be the figure needed to correct the problem of upgrading all crash barriers by railway lines.
Basically, what it comes down to is this: the insurance requirements of the railroads are the equivalent of requiring all planes to be insured against crashing into a World Trade Center.