Via the Daily Mail - A White House source told the National Enquirer that Michelle Obama has spent $10 million of U.S. taxpayers' money in the past year on vacations alone. She has taken 42 days of vacation in the past 12 months. [The expenditures include the First Lady's 68-strong security detail, personal staff, and the use of the presidential jet Air Force Two.] The Enquirer breaks down some of the expenses, but the full report can only be found in the Enquirer's print edition.
I can not confirm whether this report is true or not, but bear in mind that the Enquirer has broken a number of stories in the past on various political figures, and those stories were proven to be correct.