StrategyPage has an interesting post about the cost of stationing American troops overseas (dateline April 14, 2005).
Stationing American forces overseas has not always been as large a financial burden on the United States that it appeared to be. As the economies in West Germany and Japan recovered after World War II, they reached a point where the United States demanded, and got, payments from those countries to cover part of the expense of keeping American troops there. Since then, Japan and Germany have paid over a hundred billion dollars in such payments, and since 1991, even South Korea has made similar payments. South Korea’s payments are now $661 million a year, but are being cut 8.9 percent to reflect the withdrawal of some American troops.
They also point out that the biggest costs are travel and the economic loss of having the soldiers spend their pay in another country. Additionally, if Iraq decides to keep American troops around long-term, we should expect them to pick up part of the tab.