That's $9000/kg. For comparison the price of Gold appears to be roughly $55000/kg.
If you're right about it being as easy to grow as cabbage, then I think it could be taxed quite a lot...
My guess is the medical prescription nature of marijuana in California probably inflates its price 10x.
The justification is that this will funnel more money into the state's general fund.
And the nickname "weed" is apparently appropriate -- growers tell me it's a hearty crop.
And what is 500% tax? You pay 4x your revenue for the right to grow marijuana? It's not a tax then, it's prohibitive fine.
Take an example: water costs 2cents/gallon. a 500% tax would make water 10cents a gallon. That would be enough to promote agressive conservation, but not prohibitively expensive.
Soda costs <$1/quart at grocery, less at wholesale. But if you buy it at a restaurant, you pay >$1/pint, for 500% markup. Yet it's not prohibitve, because the baseline is sooooo cheap.
PS: There are actually huge swings in water costs in different areas, which does impact water use significantly.
Only because everybody else is growing with 0.0015 cents a gallon. If everybody was growing with 0.0075 cents per gallon, food would be more expensive, but we wouldn't suddenly be unable to feed ourselves.
PS: We are used to abundance, but there really are hard limits out there.
A lot of the world, including the country I live in, believes that products that are harmful to the society should be taxed to discourage their use. Harmful products typically include things like alcohol, tobacco, sugary drinks and candy. If marijuana would be legalized, it would certainly fall in that category. (It's important to note that a lot of the people supporting legalization don't think that marijuana is good, it's just that legalization would be immensely less bad than the present situation.)
As such, as I see it, the question of how much tax should marijuana have on it depends mostly on how much it can be taxed while still killing the business of the black market sellers.
I would like to point out that a 25% tax on legally produced marijuana is very low. A 500% tax would still be low. Considering the amounts consumed, growing marijuana is really easy and cheap. Without the legislation against it, when grown in volume by professionals it should have a cost per kg nearing that of hydroponic cabbage, or some 1000 times less than it's present street price.