Wouldn't it be much less expensive to provide each user (and dealer) with a *free* one-way ticket (sorry, not allowed to return) to the country of their choice? Hey, throw in $1000 cash with a list of "places to shop" (if you get my drift).
This would be even more of an attractive offer to those who have been recently sentenced or are currently in jail. Think they'd take it?
You're thinking too small---it's less expensive still to simply end the immoral and irrational War On Some Drugs.