Not sure. I have heard, interestingly enough, that there are federal taxes on the sale of marijuana. Which is weird, given that the federal government does not legally recognize one's right to buy or sell marijuana. These federal tax burdens are quite high, if the media reports are accurate:
There is a huge difference in taxes, WA has some ridiculously expensive recreational pot (http://www.leafly.com/stateoftheleaf). Oregon's medical prices are the lowest in the country right now, retail will be more but not that much more.
Right now rec shops in Vancouver, WA are benefiting from their proximity to Portland, but that's going to flip around once Oregon is up and running.
Are there big differences in how Washington and Oregon are taxing marijuana?