[vidarh]

A common approach is to set a fixed amount per day for expenses based on cost levels in the country in question, and be extremely strict with extras, coupled with approved supplier lists and price ranges for the actual travel.

It "rewards" those who are prudent with extra cash, and so it certainly won't be perfectly efficient, but in return it makes it harder for those who would otherwise try to abuse the system who often will go far overboard, because any extra expensive claims can be given a lot more attention (and often will require advance approval), and it drastically cuts down on paperwork.

[mattmcknight]

Amazingly, the government does that already! http://www.gsa.gov/portal/content/104877

Still they create mountains of rules....