I can say with 100% certainty that it was not costing the TTC 17$ per rider. If that were the case, the line would cost at least 250 million dollars to operate annually (including revenue from fares), or 46 million dollars per kilometer to operate annually. That number already doesn't make any sense; the crosstown will cost 80M to operate while having 3* as many underground stops and be twice the length underground. Frequencies will also be twice as high.
The TTC's conventional transit budget is about 2 billion dollars (which includes maintenance). If the rest of the budget was spent on only the subway network, it would cost the agency 25 M/km. Now how does this make sense when the rest of the network is in a far greater state of disrepair, requires more station managers per km and per station, runs trains twice as frequently, runs trains 50% larger, runs trains with twice the number of operators? That doesn't make sense, especially when most of the budget is spent on the surface network.
If the rest of the rapid transit system cost as much as the Sheppard subway costs to run, the budget would 3.5 billion, again without factoring the surface transit network, which accounts for more than half the TTC's budget.
A budget cut of this magnitude would be detrimental to all areas of the network. Wishing parts of the network away that don't have near perfect ridership is a dangerous and stupid precedent to set.