^ Hi FM!
Agreed, cuttings don't really cost much to root, so that seems like the most obvious option but I would suggest offering to return the favour the next time you/your friend grows something he/she likes. It would seem a bit mean to charge a friend just for a cutting.
I give away heirloom tomato cuttings for free to my friends, especially if they're sport individuals showing a lot of vigour. I would never dream of charging more than the cost of materials used (which is basically nothing because a styrofoam cup and a bit of growing medium costs pennies). I suggest you take the same approach for cannabis.