It depends on the quality and your location. I will try to give you averages but without getting a specific location in Washington, it’s hard to give you an exact price currently being reported. For higher grade or medical marijuana, the current price is generally $10-20 per gram, typically 30-50$ per eighth but some places as low as $20 and some strains in certain places could go for $100 an eighth, and ounces typically range from $200-$500. Keep in mind a recent flood of retailers has caused a significant plummet in prices of marijuana in Washington recently.
It depends on what your location is, whether you are using legal or illegal means, the certain strain of marijuana, and whether you have a prescription, but in general, marijuana will cost around $10-$20 per gram, $25-$50 per eighth, and $300-$600 per ounce. It is likely that if you have a prescription it would in general be a little bit cheaper.