Dare I even say the obvious, namely that the downtown should get a subway before both Sheppard and Finch? That being said, I think we could benefit from looking at Madrid, where they have an insane system built very quickly and financed through the private sector. If we could build a comprehensive enough system to attract large numbers of riders (think north/south connections as well), there could be enough money. I don't know all the details, but I think that a really good system would probably generate enough good spin-offs to the city to be worth it (increased productivity of course cannot be considered in the costing, nor can the money generated through non-municipal taxes, for instance, increased entertainment spending because people have more free time).