Yea I think a lot of guys go through this especially if you are working with good students that are scraping by with extra jobs, etc to pay for it. I would pretty much expect to charge them for .3-.5 per lesson. That's time for a proper briefing and debriefing and filling out the necessary paperwork and recordkeeping requirements for the student. We all know whose fault it will be if the paperwork isn't right. I've never had guys balk at it as long as it is fair.