I’ve been doing research on opioid-related overdose for about 15 years now (https://scholar.google.com/citations?user=YIAInOEAAAAJ&hl=en). You’re right that opioid overdose is the largest casue of accidental death in the US, having eclipsed motor vehicle deaths in about 2011. However the jump in heroin use in the last couple of years is largely iatrogenic - opioid pill prescription has been through the roof in the last two decades, and as the medical profession is having a collective panic about it (reinforced by the growth of state-level Prescription Drug Monitoring Programs, which keep track of the volume of opioids being prescribed, making a lot of docs somewhat nervous that the DEA and state-level friends are about to crack down on them), literally tens of thousands of people have been rather abruptly cut off their prescription opioids without much in the way of support or treatment for dependence. Which has rather predictably led to a lot of desperate dependent people going to the black market and rapidly discovering heroin is a lot cheaper than black market oxycontin.
ie the recent rise in heroin use has nothing to do with changes in price (and heroin has been pretty stable in the last couple of years pricewise - I’m guessing the price of heroin will drop if production increases in response to decreased demand for cannabis, but that’s an educated guess, not something based on data so far) and almost everything to do with really major changes in US policy and practice around prescription opioids.
