I recently found out about the "Drug War Clock", which estimates the annual cost of the keeping drugs illegal. The link is here. This is based on the $40 billion annual estimates from Miron and Waldock's paper.
1. Lost opportunity to tax marijuana, crystal meth, heroin, etc. These could bring in additional billions in revenue.
2. Lost economic activity to the United States by having legal production here instead of importing from other countries. Extra legal economic activity also equals more taxes, as well as more jobs.
3. Extra positive economic activity from those in prison for drug-related crimes but would otherwise be working.
The true cost could easily be double that $40 billion estimate, or $80 billion annually. While I am not a recreational drug user, it is crazy that these are illegal. This would be enormous, and doesn't even factor in the extra value society receives in terms of freedom/liberty.