Calgary has a little over a half million dwellings and at five dollars a month that would be around $12 or 13 million a year (rough estimate of course).
If 2000 trees cost the city $90,000, you could easily do 200,000 trees in one year. That would be far more than people would need, but the city does need to plant more trees along roadways, etc..
Also, it wouldn’t hurt the city to plant at least one tree in the north east. Last time I flew into Calgary and came in over the northeast it looked like Kandahar.