Why is that when a company who you have asked to help you feels like it is okay to have you pay more for something than they would themselves?
Case in point. recently had a training course (which is another topic in and of itself) on site in which we were responsible for expenses. The expenses for a 2 day training course came in at over $1000. Granted this includes flight and hotel, but it certainly wasn't an international flight, and it's not like staying in NY.
It would seem to me that normal business sense would have you charge your customer what you would expect to be charged if the roles were reversed. Just because somebody else is paying doesn't mean that there are no rules about reasonable expense. Companies would do well to set a limit for 'reasonable' and require notification/approval for out of bounds items.
Rant, rant, rant