What would you buy if you had an extra $42 billion to spend every year? What might our government buy if it suddenly had that much money dropped onto its lap every year?

For one thing, it might pay for the entire $7 billion annual increase in the State Children's Health Insurance Program that President Bush is threatening to veto because of its cost -- and there'd still be $35 billion left over.

Or perhaps you'd hire 880,000 schoolteachers at the average U.S. teacher salary of $47,602 per year.

Or give every one of our current teachers a 30 percent raise (at a cost of $15 billion, according to the American Federation of Teachers) and use what's left to take a $27 billion whack out of the federal deficit.

Or use all $42 billion for a massive tax cut that would put an extra $140 in the pockets of every person in the country -- $560 for a family of four.

The mind reels at the ways such a massive sum of money could be put to use.

Why $42 billion? Because that's what our current marijuana laws cost American taxpayers each year, according to a new study by researcher Jon Gettman, Ph.D. -- $10.7 billion in direct law enforcement costs, and $31.1 billion in lost tax revenues. And that may be an underestimate, at least on the law enforcement side, since Gettman made his calculations before the FBI released its latest arrest statistics in late September. The new FBI stats show an all-time record 829,627 marijuana arrests in 2006, 43,000 more than in 2005.

That's like arresting every man, woman and child in the state of North Dakota plus every man, woman, and child in Des Moines, Iowa on marijuana charges ... every year. Arrests for marijuana possession -- not sales or trafficking, just possession -- totaled 738,916. By comparison, there were 611,523 arrests last year for all violent crimes combined.

Basing his calculations mainly on U.S. government statistics, Gettman concludes that marijuana in the U.S. is a $113 billion dollar business. That's a huge chunk of economic activity that is unregulated and untaxed because it's almost entirely off the books.

Of course, the cost of our marijuana laws goes far beyond lost tax revenues and money spent on law enforcement. By consigning a very popular product -- one that's been used by about 100 million Americans, according to government surveys -- to the criminal underground, we've effectively cut legitimate businesspeople out of the market and handed a monopoly to criminals and gangs.

Strangely, government officials love to warn us that some unsavory characters profit off of marijuana sales, while ignoring the obvious: Our prohibitionist laws handed them the marijuana business in the first place, effectively giving marijuana dealers a $113 billion free ride.

Despite all that, we now arrest one American every 38 seconds on marijuana charges. And we do so at a staggering cost in law enforcement expenses, lost tax revenues, and staggering profits for criminal gangs.

The alternative is clear: Regulate marijuana just as we do beer, wine, and liquor. The only thing lacking is the political will.

Rob Kampia is executive director of the Marijuana Policy Project in Washington, DC.