Currently, smallpox is one of 12 pathogens that the U.S. has classified as being a possible material biothreat to the country. Because of this, the government is in talks with Siga Technologies Inc. to buy $433 million worth of a smallpox drug to add to the country's biodefense arsenal. This would buy 1.7 million doses, which comes to about $255 per dose. The drug in question is called ST-246, and it's an antiviral pill that is designed to be taken if a person has missed the window for inoculation after being exposed to smallpox. However, is hasn't been tested on humans, for obvious ethical reasons, and the jury is out as to whether animal testing would prove anything where human effectiveness is concerned.
The United States currently has $1 billion worth of smallpox vaccine, which is enough to vaccinate the whole country. However, it has to be given within four days of exposure to reliably save lives. In contrast with ST-246, this vaccine costs only $3 per dose.
This deal is surrounded by political controversy, as some consider that the deal is more of a political alliance than a national security plan. Additionally, some scientists think that it's an enormous waste of money to buy this much of an untested vaccine in defense of a threat which may never appear.