Depends how its grown. RAND estimated somewhere around "225 per pound for a successful, wellmanaged
operation, plus in-kind contribution of labor...". This was done in 2010 and so its a little outdated now but still a great read.
http://www.rand.org/content/dam/rand/pubs/working_papers/201...
If your forced to grow it inside a building, under artificial lighting, with heavy security and heavy regulation; then yes it's ~15$ / oz (225 per pound). Cut out that crap and use a field and it's far cheaper.
PS: I don't smoke and have no idea if 'hydroponic' is better for the plant or if it's a proxy for grown in the US and fresh. But, I suspect it's mostly about post processing.
There's 450 grams in a pound. 225/450 = $0.50/gram.
But that number and mine is nonsense. I was being generous in order not to shock anyone. Look up the price to grow crops like corn, cotton, etc. It's < $500/acre. Per acre. When cannabis is grown like every other crop it becomes dirt cheap. Great cannabis does not need to be grown indoors. Great weed is grown outdoors on the west coast all the time.