From Forbes:
One black-market dealer tells The Pueblo Chieftan he sells high-quality marijuana for $225 to $300 an ounce, compared to $400 or more charged by state-licensed stores. “People will get real tired of paying the taxes real fast,” he says. “When you can buy an ounce from me for $225 to $300, the state adds as much as $90 just for the tax.”
Adult Coloradans can grow up to 6 plants of the best stuff in the world with virtually zero chance of being arrested. If people in CO buy it on the black market, it will be from a local Mom & Pop grow your own enterprise, not the cartels.