At least where I live in the Dallas area, most of the photos that go into the year book are taken by contracted photographers. The school I teach at (my full time job) has Lifetouch or Prestige do the yearbook stuff. They have to have the yearbook photos by them. On the flip side for lifetouch or prestige is they have to do those yearbook photos for free and then try to sell packages that I think are outrageously priced. Yes it's a jungle and can get down right bloody but it's a hobby for me so I don't fret it too much.
I was about to ask what they charge. I have heard that the school senior photographers are pretty cheap compared to us quality shooters, and I've heard that they are crazy expensive. I figured it might be relative on income.
I think $500 for a senior session might be cheap to many photographers here.