[Zanta]

I'm finishing the book Dreamland, by Sam Quinones, which directly addresses your questions (with a particular focus on addiction in middle america/appalachia)

Q1: Medicaid co-pay for $1000 worth of OxyContin was (as of ~2014, might still be) on the order of $3-5. Those unable to get prescriptions fence stolen goods, primarily from rural WalMarts

Q2: Opiods are chemically similar to heroin. Addiction is severe and enslaving. Someone who wouldn't get off the couch to throw out the trash will walk miles in a snowstorm to get their fix.