Amtrak bought 70 pure electrics for $466M USD. AMD paid $223M for 20 dual modes, admittedly more expensive but more versatile too. Let's say an added $80M on a 20-unit order. That's small change for ML.
For RER, the answer may be EMU's....Chicago is currently accepting 160 Silverliners which cost $577M USD.
UPX is the sure-fire winner for quick electrification. Extending the wire to Bramalea wouldn't cost much incrementally. Dual Mode would get you to Mount Pleasant and Kitchener.
You won't electrify LSE until the added track gets built and a new signal system is installed (you have to electricity-proof the signalling before you can run electrics). Same with Unionville and Barrie. (Let's hope their new signal systems are already electrification-compatible). Georgetown and Milton have conflicts with freight operations, as does Richmond Hill ...... CN will insist on an over/underpass there. I don't see how the civil work on these lines can be fast-tracked in time to electrify before the next elections.
You could probably advance design to the point where you could complete procurement before the elections. With the right cancellation penalties, you could probably be confident that these aren't going to be undone by the next government. But that's an unpalatable repeat of the Hydro gas plant debacle, and it's optics, not opening day.
- Paul