I am thinking of alternatives to the Sheppard LRT plan, that might be better received by the public and politicians in Scarborough, but do not cost way more than the said LRT.
Option 1: Build Sheppard LRT, but use high-floor vehicles that can easily fit into the existing subway tunnel. Most of the new tracks will be on surface.
That would cost somewhat more than the low-floor LRT plan, since the surface stations will have to be more elaborate in order to be accessible. But it still much cheaper than a subway extension, and the LRT can reach the east end of Scarborough, unlike the subway that can only go as far as McCowan or STC.
Option 2: Defer transit improvements on the central section of Sheppard, and build a shorter LRT that connects the Scarborough Subway terminus with eastern Scarborough. The line would start either at Sheppard & McCowan, or at STC; and go to the Zoo, with a branch to Malvern Centre.
That would improve transit in the east end, while keeping the Sheppard subway dream alive (though no actual subway extension anytime soon).
Option 3: Build BRT on Sheppard. This is a cheap option, and keeps the Sheppard subway dream alive (smaller sunk cost for BRT, hence more chances for an upgrade to subway, theoretically). The only problem is the Hwy 404 crossing and the connection to Don Mills subway. That connection is easier to build properly for the LRT than for the bus.
Option 4: Defer Sheppard altogether, and build the "Scarborough-Malvern" LRT, as has been already suggested here. That will be a very useful line indeed.
With enough money on the table, Option #4 may even be combined with #2.