The problem with taxing something you don't like is the government quickly becomes dependent on the revenue and ends up having a perverse incentive to promote it.
My guess is the medical prescription nature of marijuana in California probably inflates its price 10x.
We just deregulated alcohol last year -- meaning the WA liquor control board stores shut down and we can purchase from grocery stores, with a $2.85 tax per 750ml, on top of the 10% sales tax.
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.
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...