And while some evidence indicates that the tax-related markup on legal, recreational marijuana has driven buyers back into the black market, the average price per ounce looks to support the idea that legalization drives down prices. 

As you can see from the map below, the mean price for an ounce of marijuana in the United States is $324, according to the subtly named "PriceOfWeed.com", a site which crowdsources average prices from users across the US, Canada, Europe, and Australia. Not coincidentally, the states where prices are lowest are also the states where recreational use is legal.

As a side note on taxation and legal marijuana, it appears that while some legal weed proprietors are happy to pay their fair share, the inconsistencies between state and federal laws make the reality anything but equitable.