Every state that has allowed the opening of medical marijuana dispensaries has gained tax revenue while seeing an increase in jobs. You might as well ask whether pharmaceutical factories making ibuprofen and antibiotics are economical; obviously they are, and any politician would be glad to have such a factory start up in his or her district, adding jobs and valuable tax revenue. What we should really be asking is whether paying detectives to track down sick people and even recreational marijuana users is economical - society gains little or no benefit from such activities, and in fact is likely harmed.
No, medical marijuana dispensaries are not economical, because they take advantage of people who need help. The dispensaries operate for profit, and they raise their rates on people or charge them a membership fee in order to have access. It is more economical for a person to find a supplier who can work with them directly.