One would hope that the "vertical" thing would take care of part of the land costs. Especially if you can stick your setup right on top of an existing building in a city.
Farm land is much much cheaper, atleast in my country. Moving the farm to the top would mean you can have just one floor of plants. Cooling costs will go up (many hydroponic farms are rather going underground) and so will electricity which is higher in the cities.
Countering, lighting costs can be lowered by using sunlight to complement. CO2 levels are higher in city, might help plants grow faster (and maybe thinner?). Transportation costs of produce will go down as they don't need to be transferred 100s of kilometres.
We need a few experiments to figure out the logistics and economics of it as there are multiple factors.
Farmland is only cheaper because externalities (financial, social, environmental) aren't reflected in the cost. Vertical farming is supposed to solve more problems than just "well, we have limited space in a city".
