Most of the serious addicts I’ve known get the vast majority of their money through theft, so in some ways the do have unlimited resources, if the price goes up they just steal more, which means you get MORE drug related crimes and costs to society.
Drug addicts are not master thieves. They are very limited in their ability get money by theft.
They usually don't think very clearly. Plus, people can usually spot them from a mile away and recognize them and prepare to prevent theft. Drug users usually get arrested quickly and then identify other drug users and drug dealers.