Hmmm... 10b.
1.) DRL Phase 1: Don Mills and Eglinton through Pape to Eastern (maybe with an 'elbow' down into the Portlands & Donlands proper) then across Adelaide to somewhere in Clubland through the financial district (clubland because restarting subway construction @ Bay/Adelaide would be a pain, clubland should have more room). Length of about 12-16km, depending. I wouldn't use current "subway" tech either, but something more akin to the RAV in Vancouver. Cost should be about 1.8-2.4b (@150m/km - RAV was 80m/km).
2.)New "Rapidbus" network: I described what I had in mind earlier. I don't really know the bus network well enough to pick and choose which routes would be best but high ridership arterials like Dufferin seem like shoe ins. Given that I don't know the exact routes, lets assume that 200 new high capacity articulated buses are necessary. At a mil each, we are at .2b. I would add another 300m here for what the TTC claims a RFID card system would cost, allowing all door boarding (there are other ways, but whatever). Maybe another hundred million in route upgrades (diamond lanes, improved stops stops, signaling systems, road layout modifications plus bus station modifications to handle bigger buses). Should work out to about .6-.7 billion for the whole kit. Run these as a different brand. Differentiate it from vanilla buses to boost attention. Use different colour schemes, unique buses and maybe more comfortable seats.
3.)Eglinton RT Phase 1: No matter what, totally grade separated between the Humber river & Don Mills. This is one of those "LRT vs. world" debates, but the central section I am talking about here would be more or less the same regardless of what was chosen. I'd opt for RAV like technology, a mini-metro. At what should be no more than 150m/km for about 13km we get 2b, give or take.
4.)Sheppard East RT: Basically complete the Sheppard to SCT. For all I care, build the thing above ground on a viaduct. Anything to get away from the TTC's costing of subways at 400m/km or whatever the number is today. There is no way this should cost more than 2b.
5.)Finch Hydro corridor Transitway: Pretty self explanatory name. I doubt we will ever see bus lanes along the 401, so this could fill in for that. Might be better anyways, the 401 isn't really integrated with high order transit anyways, this would easily connect to the current Finch station, as well as the planned Finch West. Length of about 30km, the costs can't possibly be too high. Just to be on the safe side, assumed cost of 50m/km for about 1.5b.
6.)Eglinton West Transitway: Richview corridor to the airport, baby. Land aquisition costs have gotta be non existent. Basically as per the original Network 2011 plan. Shouldn't be more than 600m. In the interim it should have its eastern terminus interact with GO services along the Weston corridor as well as the Eglinton RT.
7.)East End Transitway: This I'm not sure about. The idea would be to build a transitway along the hydrocorridor running N.E. from Vic Park/Eglinton to the Rouge River ravine. I don't really know Scarborough so well, so maybe this isn't even necessary, but it could provide a highspeed direct busway (hell, maybe let cabs use it) between the boonies and the northern end of a DRL, as well as the DVP for GO buses heading to Union. Call it 900m.
8.)DRL Phase 2: Picking up on Adelaide in Clubland somewhere, this would run to somewhere along the Bloor line. Traditional routes run basicly to the rail corridor then up to Dundas West, I'm personally partial to Dufferin. The western leg of the DRL isn't really meant to "relieve" anything, so I don't see the harm in having it do a milk run up Dufferin to Bloor to start with, then up to St.Clair/Dufferin before veering off to the Eglinton BRT/RT/GO junction around Eglinton/Weston. About 1.6b.
All in all this is closer to 12b, but parts of it may not even be necessary (East End Transitway, RFID card system), so I think it is fairly comparable to the current TC in costs. I didn't include projects funded under MO2020 like improved GO services or independently funded TTC projects like the waterfront east LRT. Its a pretty bus-heavy system. There are routes like the Weston corridor which might be neat to run with a kind of tram-train setup, but might be a bit overkill with both a western DRL leg and better GO service. Maybe in the future it may be worth converting some of the busways to LRT, but whatever.