Someone with heavy, habitual alcohol use can still get drunk on $20 of alcohol. Someone with a heavy opiate habit may spend hundreds of dollars a day on drugs just to maintain. A habituated opiate user could also get through the day with $20 worth of drugs if we allowed opiates to be produced and sold like alcohol, but we don't. So the unemployed junkie needs to beg or steal a lot more than the unemployed alcoholic to get their fix. That's why the parent comment highlighted "illegality of the drugs" as the cause.