You should expense (to the IRS) what the actual expenses are, but you can charge your client whatever you agree on.
e.g., a month ago someone wanted me to travel to their site.
Although I didn't end up going, my fee to do that would have been much more than just the travel (6 hour drive to another state) and hotel costs: I also have to factor in that while I'm travelling, those are hours I can't bill to any other project, so the client would have been billed for the full two work days of travel even though my out of pocket costs would have been much less.
Exactly. Every time I travel for a client they pay for everything, plus the "sandwich & juice" in the airport, taxis/trains to/from home/airport/hotel/meetings AND the hours/days from the moment I exit my home to the moment I reach the hotel. For the return, any minute after 5pm, until I get back home.
I am not willing (in order to be 9am on the client site (in another country) to spend half a Sunday away from home and loved ones for free. I usually charge 1h commute +2h in the airport pre flight + duration of flight + commute to hotel post flight.
e.g., a month ago someone wanted me to travel to their site.
Although I didn't end up going, my fee to do that would have been much more than just the travel (6 hour drive to another state) and hotel costs: I also have to factor in that while I'm travelling, those are hours I can't bill to any other project, so the client would have been billed for the full two work days of travel even though my out of pocket costs would have been much less.