Marty over at Laneway Housing Advisors published this listing in his newsletter today. It's for an entitled lot at 78 Gladstone Avenue in Toronto that has been approved (by way of a minor variance) for 6 units. Five units in the front where a house currently sits and one unit at the back in a standalone laneway suite. Though it also happens to be a corner lot and so the laneway suite isn't really "in the back".
It's listed for $2.5M. And according to the description, you can build about 5,500 square feet (4,200 sf in the front with a 1,300 sf laneway suite). This ask translates into a land cost that is just over $450 per buildable square foot, which is far more than what high-density land typically trades for in the city right now. This is usually the case for smaller low-rise sites.
To help put this figure into some kind of context, Bullpen Consulting published in their latest insights report that the average high-density land price in Q4-2021 was $135 per buildable square foot in Toronto (416 area code only). Of course, averages only tell you so much. To truly evaluate the feasibility of a site like this, you'd need to create your own pro forma and do your own residual land value calculation. The value of development land depends on what you can build on it.