It really is just what you can afford. I would love to give my nieces and nephews more, but I have 27 nieces and nephews, with a graduation a year until 2019, some years, we have multiple graduations, and in a few years, HS graduation will be next to college graduation, and then the weddings will be starting soon, I am sure.
I have to keep it low, and keep it the same, so I give a crisp clean $50 bill.