Is there a correlation between pharmaceutical prices and drug dealers? Question: Is there a quantitative or some kind of correlation between the number of drug dealers in a certain region and the price of pharmaceutical drugs?

This is for a case I'm working on, but I can't seem to find a direct correlation between the price of prescription drugs and drug dealers.
Right off the bat, it seems simple right? Lower prices force drug dealers out as consumers turn towards the brand name drugs which effectively lowers the amount of drug dealers in an area. However, I can't seem to find, anywhere, that says something along those lines.
Direct correlation seems unlikely. You would probably have to control for population or even better, population density. Leaving prices unchanged a city with ten times the population can support ten times as many drug dealers. Differences in average income levels would present a similar problem.

Finding reliable data, such as number of drug dealers and a good measure of price levels will be a challenge as well.