For sure street drugs are overpriced vis a vis what they sell to the end user for, but that gives them all the more room to lower price to capture a certain share of the market if they have to compete with legalization. 

The government's desire to take their share via taxation, as they do for liquor (what's the total govt markup incl tax on a bottle of $15 wine - about half?), will ratchet up the retail price.  Colorado, Washington, and Oregon have all had to look to reduce  initial 30% government taxation on pot, as the black market was still competing.

The reason why I mentioned prescriptions, is because  control is what is being recently advocated.  Doctor vetting, patient programs, counselling, and a control method of receiving free/subsidized heroin.    

We are still waiting to see pot decriminalized and legalized. If Trudeau does not get it done under his mandate,  there is no way this will happen under the PCs, let alone legalizing other recreational drugs.