I grow some of the best and most unique bud in my area. When pot becomes legal I will either not have to drop my prices because of quality or I'll just be able to grow more and charge less and people will still buy it because it is the best around. Pretty simple really either bring the A game or go home.
"Legal" covers a pretty broad ground.
Forgetting for the moment that cannabis is still illegal everywhere in the USA under Federal law, even in CO, where recreational cannabis is now "legal" you can't grow nor possess as much as you like, and sales are heavily restricted. So even "legal" cannabis is still controlled to the point where prices are artificially high.
Its doubtful that cannabis will ever become truly unregulated, say the way it was 100 years ago, like tomatoes where you can grow, buy, or sell as much as you like. People will always pay more for the best of the best, but if cannabis were truly "free" (ie not tied up by law), the stuff would cost as much as any other spice or dried flowers. . .ie tens of dollars per ounce, not hundreds of dollars.
Edit:
Lets put it this way. If cannabis were truly "legal", you'd be allowed to plant 1000 acre fields with 100,000 plants in them. . .and plenty of farmers would actually do so. Medical cannabis would be a viable legal cash crop like corn, soybeans, or cotton, with roughly comparable pricing. In fact, I think on a yield/acre basis, cannabis flowers would probably be cheaper than cotton (which currently costs under $1/lb). Under that kind of regulatory framework, high grade hash could be made in commercial quantity and could be so inexpensive that many people wouldn't even want to smoke buds at all.
Again, of course there is always room in any marketplace for the "best" and if you were growing truly top grade organic stuff, people would pay a premium for it. . .but the market ultimately determines what that premium is. If decent quality mid-grade commercial bud cost only $10-20/ounce and you can grow whatever you like in your backyard in whatever quantity, I don't think there are going to be many, if any willing to pay $150/ounce for top shelf stuff.
But all this is basically a "pipe dream". There is far too much money to be made selling and taximg weed for any powers that be to truly re-legalize it. (IE nobody thinks that the taxes on cigarettes are going to go BELOW their currently greater than 75% level). I think the best we can hope for is some sort of comprehensive decriminalization so that people who want to smoke/use it or grow it in limited quantity. can do so without fear of criminal sanction.