Black markets would be "playing a cat and mouse game" with Government. That increases costs and reduces efficiency. Anarcho-Capitalism, would be more efficient, in that case.
The costs are marginal, given the inherent inefficiency of The State.....I can think of no better example than legal marijuana being more costly and of no higher quality, than that acquired from the local hippie pot head.
Raising the stakes with even more State aggression (i.e. the drug war) only serves to squeeze out the more peaceful elements in favor of violent thugs, for whom life is cheap to begin with,