Mayor John Tory brushed off ballooning costs for the Scarborough subway extension, insisting that the controversial project would go ahead in spite of a $900-million jump in the price-tag.

The one-stop subway extension to Scarborough Town Centre, a pared-down version of the original plan, is now expected to cost in the range of $2.9-billion. Only months ago the project was expected to cost $2-billion.

Mr. Tory insisted the project would be built, along with an extension of the Eglinton Crosstown light rail line that is also rising in price.

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"They cost what they cost," the mayor told reporters at an event in Scarborough. "There is nobody that is talking about doing anything that is less than responsible."

But councillor Josh Matlow shot back that it was time to "get real" on the question of transit for Scarborough.

"Let's move forward now with an honest transit plan that's responsible with tax dollars," he said, predicting the debate would return to city council.

"City hall has a choice to make. It can either take the positive, honest approach that will put people before politics -- or do the exact opposite. And I encourage residents of Toronto to make their voices heard.

The cost figures come only weeks after the city revealed the proposed subway would carry just 7,300 people at peak times, about half the ridership expected when the subway was first approved.

The original price tag was based on a limited understanding of what was actually involved. It was an estimate based on the cost of the Spadina subway extension that did not take into account specific factors in Scarborough.

An analysis in Scarborough showed that the topography would require deeper tunnels in some places. The stations themselves would have to be 45 to 90 per cent deeper than thought, raising their construction costs immensely. And the high water table of the area would require more concrete than expected.

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The result is daunting budget math. The original proposal for a three-stop subway had a budget of $3.56-billion, a total which was funded by the three levels of government. Planners then proposed cutting the subway back to a single stop and extending the Eglinton LRT with the savings. They said both could be done within the original budget.

The new figures show that the two projects together would cost $4.5-billion, leaving a $940-million hole to be filled. Mr. Tory said he would push to involve the private sector, in an effort to trim costs. Former mayor Rob Ford also argued the private sector would help build this subway, but was unsuccessful in finding backers.

Transit for Scarborough has been a political football for years. The province offered to pay the entire cost of a light-rail line to serve the area, but city politicians – convinced that subways were superior and that Scarborough deserved the same transit as central parts of the city – insisted on replacing the project with heavy rail.

To pay for the much more expensive project, the city passed a 30-year levy on homeowners and tapped the federal government for funds. The city also assumed responsibility for operating expenses and any changes in cost, both of which the province had promised to cover for the LRT.

During the election campaign, Mr. Tory promised not to revisit the controversial decision. Earlier this year, though, he threw his support behind the proposal to keep the subway but make it smaller and add to the LRT. This allowed Mr. Tory to argue that even though he was changing his position, he was providing even more transit to the area.