What should I charge a student staying with me?

[LaBelleDameSansPatience]

We are hosting a 17-year-old French student who will be doing work experience in a local collage. He will be staying in our (not exactly well-maintained) caravan, needing to come into the house for toilet, shower, etc. I will obviously not charge anything for this!
We will be driving him to work and feeding him, he'll be using electricity etc. His parents want to know what we will charge him for the 3 weeks. I have no idea. Don't want to make money out of him, but also don't want to be out of pocket.
Has anyone any idea?

Maybe just ask for a contribution towards food etc?

I find it hard to judge as it depends on what you normally spend etc. In any case, most people tend to be very generous when asked for a 'contribution' as they want to show their gratitude.

£20 per week?

Depends on how you know them / what the relationship is.

If I had offered to look after a friend's ds for a couple of weeks whilst they were alone in a foreign country, then I wouldn't charge them anything.
If it were someone who know someone who knew someone and they were expecting to pay rent etc, but I was saving them from hotel costs by offering a slightly dodgy roof, but also chauffeuring and food, then I'd probably be looking at around a tenner a day.

Thank you. Have never met this boy … he is sent by our partner college in France … good to have some ideas!

Do the colleges not have suggestions? What do the French hosts charge? Who has done this before where you work? Ask them.