This is a subject that I really find fascinating, because there's really nothing that I can think of to compare it to in the past 50 years...
Both Washington and Colorado have legalized marijuana, and as a result, something that used to be totally black market is now becoming a legit industry -- I believe Colorado now has a Marijuana Czar as a state official to overlook the whole thing. I bet Yakov Smirnoff has a good joke about that in Branson, but I digress.
Washington is planning a 25% tax on each of the grower, the processor, and the distributer. There will also be the sales tax on the last leg of that (8.75), so overall it ends up being around a 45% tax to the consumer (I've heard as high as 58%, but there's propaganda on both sides of this debate.) So the problem there is that a legal ounce is estimated to cost you $482 in Washington ($723 in their worst projection, citation below), but the black market is running less than $250 an ounce.
I think states have looked at tobacco as the industry to mirror with this... Washington charges about $3 per pack as state tax. I think the thing they are overlooking is that there was never a black market infrastructure in place to handle moving tobacco... it has always been legal, and until the past twenty-five years or so, it really hasn't been taxed severely. I am sure there is some sort of black market for cigs in Washington btw, I just don't think it makes up a very significant percentage of total cigarettes consumed. If I am wrong, I apologize.
For pot, however, all the black market infrastructure is in place, and probably in place pretty well. If the difference in price ends up being nearly double, I can't see people leaving their current source in order to go shopping at some store. Once you buy it, will there really be a way to tell that it's legal vs. illegal? Personally, I would think it better to set a fixed amount per ounce -- say $30? -- that goes to the government. Let the market decide what the price should really be... if it ends up balancing out where a legal store sells it for $280 an ounce and the black market sells it for $250 an ounce, people may consider the cost worth the price of avoiding any hassle from an illegal purchase. Once you are able to break down the cost benefit of running the black market for a while, and it slowly decays, you can raise those costs and you don't have to deal with fighting an established distribution chain.
Cite:
http://www.forbes.com/sites/jacobsullum ... gislation/