Here in Washington State where a few recreational pot stores will open next month, it appears that state-taxed sales will be priced much higher than street drug sales. I think chronic users will stick with their illicit sources and be entirely unaffected by the new law. Sales and possession to/by youth, growing, public smoking/vaping and possession of more than one ounce of dried product per living unit are still illegal.
Some say that, some say otherwise:
'As Washington's so-called "pot czar," UCLA public policy professor Mark Kleiman has furnished the state’s Liquor Control Board with policy recommendations. [...] Many people in Washington have worried it will be too high, making it uncompetitive with black market pot. [...] Kleiman guessed that once the market stabilizes, producing a gram of marijuana could cost as little as 50 cents. Even adding taxes and profits margins could price it well below what illegal pot costs.' - http://www.kplu.org/post/washingtons-pot-czar-says-legal-marijuana-could-be-too-cheap