SpecialDiva,
Exactly what Amy said. If a client wants to take you away, they pay for everything, not just the holiday itself. Not only is the flight (or train) paid for, but I expect my travel to and from the airport/train station at both ends to be covered plus a little extra for expenses at the airport. If it is a long haul trip, I stipulate business class but offer the option of flying out a day early in economy plus a night in a hotel room by myself (I also charge my day rate for this.) Often it works out cheaper to just put me in business class.
For my fee, well, it’s completely up to you. I operate a sliding scale - the longer our time together, the more economical it is. One day rate is my overnight rate plus 50%, two day rate is one day rate plus my overnight rate, three days is x3 overnights plus a bit more. Anything longer is negotiable although I won’t do anything longer than 5 days unless the client books a suite and I have my own room.