John Fund in the Wall Street Journal:

The total cost for congressional overseas travel is never made public because the price tag for State Department advance teams and military planes used by lawmakers are folded into much larger budgets. Members of Congress must only report the total per diem reimbursements they receive in cash for hotels, meals and local transport.
They don’t have to itemize expenses—a convenient arrangement since most costs are covered by the government or local hosts. Some trips subtract some hotel and meal costs from the per diems, others do not. “The policy is completely inconsistent,” one House member told me. Total per diem allowances (per person, including staff) can top $3,000 for a single trip. Unused funds are supposed to be given back to the government, but congressional records show that rarely happens. . . .
The flap over the now aborted Gulfstream purchases could shed light on just how big Air Congress has gotten. The executive branch routinely goes along with whatever Congress wants to spend on itself. This year legislative branch spending is up more than 10% over last year.