Ehh, drugs arn’t cheap, even Cocaine used to exclusively be a vice of the wealthy until cheaper variants and derivatives like crack were created and flooded into the market.
Additionally the Junkie seems to be a user of the pure stuff, not black tar or freebase, The sort of stuff you’d get from a medical supply. I’ve always figured the Junkie was one of those ‘upper class’ drug using types who just happened to be in the shelter when it all happened because the things make great places to shoot up.