For now, prices are high: around $20 a gram, which is twice the black-market (or medical) cost. That partly reflects eye-watering excise taxes: 25% at each stage of distribution, plus normal sales taxes. But wholesale prices are high too, suggesting supply shortages are the main culprit.
There is more here, from The Economist, much of it deals with how far the United States is from having truly legalized marijuana. [Note: an earlier version of this post mistakenly referred to Colorado.]