According to Tom Coburn’s office (as relayed by the State Department in response to a Coburn query):

The State Department expects to spend over $28 million on 2,216 conferences in 2006. This is down slightly from the $30.1 million spent
on 3,024 conferences in 2004 but up significantly from the $17.9 million
spent in 2001….
In 2004, the federal government spent over $300 million on conferences.