The cost was determined during a study 10 years ago. The study is
HERE. The important pages are:
- Page 23, Mississauga's Rapid Transit route from Renforth Gateway to Malton GO.
- Page 29, Diagram of the three options (HSR capable through route corridor, spur usable only by smaller trains, and AGT (people mover) to the Georgetown corridor and Eglinton-Renforth intersection.
- Page 31, Only airport shuttle, AGT (people mover), and transit can get direct access to the terminal without a corridor diversion. Only the corridor diversion will get HSR, VIA, and GO to the airport without taking the AGT (people mover) to the rail corridor.
- Page 33, cost of corridor diversion in 1994 was estimated to be $900 million.
- Page 36, of the short listed options the people mover (AGT) to the rail corridor is the most affordable option, and the only one with GO, VIA, and HSR link potential.
The summary of the report focused primarily on the people mover (AGT) option but also mentioned a rail spur ending at the long term parking with everyone transferring to the AGT there. The reason they didn't mention a direct connection to Terminal 1 was the complexities of connecting a true heavy rail corridor to the terminal with the roadways, AGT, and terminal developments occurring there.
In the current Air Rail plan they take the link right to Terminal 1 but there are serious tradeoffs in cost (the extra cost which will be significant since it is completely elevated), rolling stock flexibility (the route is curvy, steep, and only handles a very small trainset), and scheduling flexibility (the track will not be twinned). With the plan to stop the spur at the long term parking area the cost was much less and there weren't the same limitations on rolling stock and the line was twinned, but the benefits over the people mover (AGT) to the Georgetown would have been much more marginal.
The report is clear that if the goal is to connect GO, VIA, and potentially HSR to the airport the only options are the corridor diversion for $900M in 1994 (deemed expensive), or the people mover (AGT) to the rail corridor. It is also clear in the report that the people mover (AGT) connection provides the most beneficial link between local rapid transit and the airport.