..... Most weed is grown in comparatively small batches and has a market value to reflect that. Imagine growing greenhouses full of weed, with the associated drop in cost and selling it at half the present price including tax - easily achievable.
Trust me, its not the quantity or volume of it that makes it expensive... its because thats what they suppliers/growers etc can charge
I knew of one place in my dim and distant past (nowt to do with me, Big Brother if you are watching this conversation!) that was able to turn out more than you could ever possibly have imagined possible... didnt stop it being sold at the same price as a student with 6 plants in his wardrobe.
The black market does not operate by normal supply and demand rules
As soon as some form of persoanl quota or alloawnce for specific substances comes out, as has been suggested, THEN you will see prices plummit, and with them quality and purity... then you've got even more smacked up junkies with bleach poisoning to deal with than there is already