After having some recreational drugs in the past, we started talking about all the money we spend for it. About 200$ a month equal = 2400$ a year

so 2 400$ x 1 000 000 = 2 400 000 000 = 2.4 billion dollar a year tax evasion
the drug traffickers does not pay taxes much
Also in Europe criminal drug related business is estimated about 60 billion

Is it a conservative number?

I do not know

How much money is spent on war drugs? 30 billion a year

So most of the money is paid by the tax payers who does not use them.

They could be used for health, science, schools, infrastructure, and other complicated