That has no bearing on electrification or infrastructure costs.
East coast mainline? Electrification started over 40 year ago! The pricing I've seen is in 1983 currency! If that's the kind of thing that's been using for price estimation for anything current, it's no wonder that estimates are woefully low! There's probably some fool out there inflating this ancient numbers, using very different building practices, using consumer price indexes, rather than construction or tender price indexes!
It costs what it costs, and if an incompetent idealistic fool is going to try and use ancient data and massively optimistic assumptions to keep prices low, then we'll see a massive cost-overrun ... which seems to be par for the course in Montreal engineering circles.