One of the advantages of living in a state where marijuana has been legalized — either for recreational or medical purposes — is that the cost of cannabis is generally lower than in places where the substance is still criminalized. The average cost of an ounce of weed in the U.S. is $324, according to PriceofWeed.com, but as the legalization movement spreads, more states are bound to see their prices drop.

RELATED: 5 Countries Where Marijuana is Cheapest and Most Expensive

It's no coincidence that some of the highest prices are found in states and regions that have largely restrictive marijuana laws. In much of the Midwest, South, and Northeast, marijuana is illegal on both a federal and state level, allowing the black market to thrive and control cannabis pricing. When dispensaries are introduced to a state, however, free market competition appears to drive prices down, Forbes reported.

Here's a map that identifies the price of weed in each state.

Forbes - forbes.com

It makes sense, after all. Marijuana users aren't criminals — many are legitimate medical patients and others are simply users who enjoy cannabis responsibly and recreationally — and nobody wants to operate on the black market, putting themselves at risk. Given the opportunity to purchase marijuana legally at a certified dispensary, many users have seized it.

"In four states where pot has been legalized or decriminalized — Washington, Oregon, Colorado and Alaska — the price of an ounce has fallen below $300, compared with the nationwide average of $324," Forbes reported.

The map above uses data from the website, PriceOfWeed.com, which relies on information from users who have purchased cannabis, both on the black market and at legal dispensaries, and report the price anonymously. It shows that Oregon, a state that legalized recreational marijuana, has the cheapest weed ($204 per ounce), whereas North Dakota, where marijuana is strictly prohibited, has the highest price ($387 per ounce).

For reference, an ounce of marijuana could be ground up and rolled into about 60, average-sized joints.

Despite some anomalies — e.g. in D.C., where marijuana was legalized for recreational purposes, an ounce costs $347 — the trend appears to be consistent. While cannabis is typically more expensive at dispensaries in legal states than the black market, that's because the consumer appeal of operating in a legal market has put pressure on illegal dealers, forcing them to charge less in order to maintain their clientele.

RELATED: Mexican Marijuana Farmers Are Losing Profits in Light of U.S. Legalization

A similar trend is happening in Mexico, where drug cartels have been forced to pay marijuana farmers less in recent years due to legalization efforts in the U.S. It's one of the most common arguments in support of legalization: If you want to take money away from criminal organizations that traffic drugs, legalize pot and let the states regulate it as it has with other recreational substances such as alcohol and tobacco.