A couple billion dollars divided by the number of houses in LA... actually wouldn't add that much value to the housing prices. After all, the total assessed value of real estate in the county is about $1.7 trillion.
As best I can figure, America's land alone is worth somewhere between $22-44 trillion, and that's not including any of the buildings. (Manhattan's land alone is worth about $1.7 trillion according to my sources)
Does it even make sense to divorce the price of land from the buildings? Developed farmland also has a different value from virgin land, but the difference is ignored.
Manhattan's land would not be worth 1.7T$ if it were just farmland.
Of course you can approximate the price: For each plot of land you consider the value under the counterfactual where any buildings on it weren't there but all the neighborhood surroundings were unchanged. The sum across all the plots in the city is the total land price.