During the Metrolinx meeting today McCuaig said that electrification would cost $10 - $12 billion (rough estimate, actual costs to come by September).
I don't see that at all. Given all day 2 way service is set to cost $3 billion according to the Cost - Benefit studies Metrolinx has done on them, and the average of $16-$18 million per KM (coming from the $1.8 billion for Lakeshore electrification and $450 million for UPX electrification) for electrification, it should work out to around $8 billion (assuming electrified service terminates as Mount Joy, Richmond Hill, East Guilimbury, Mount Pleasant, and Lisgar). Add a billion for the Union Station tunnel, and you still only get around $9 billion.
Maybe they are counting the Electrification to Kitchener, Niagara, and Barrie, I don't know. those portions would come from the "outside of GTA" pot anyway.