We do quite a few of these in the course of a year, both for college applications and for sports scholarship applications. Editing is editing -- we charge the same for doing this as we do for everything else we edit.
I've done about six of these. I knew the kids involved, so I did it for free. It made a BIG difference for them. Two of them got sports scholarships at Division I schools, even though we are a Division 4 high school. Don't get me wrong: I'm not saying my talent had anything to do with these kids getting into school. What I AM saying is that sports highlights DVDs -- whether edited by Spielberg or by me -- make a big difference in the admissions process.
If you charge, use the same formulas you use for any other work.
That's going to be a tough one since it depends on your market and you are going to have some potential issues with people taking you seriously because of your age - although more and more I think folks are looking at youth as being technically savvy.
You could go the Videoscout route, which is $999 for a complete package that includes videotaping a game, a practice an interview with coach and player and then putting that all together on a CD. Or you can go by the hour using material provided by the parents (since in their opinion, their video material is at least every bit as good as what a professional would shoot).
I started out doing $55/hour for editing and in my market couldn't find people that would take me seriously. Raised rates to $75/hour and am getting more customers than before (go figure).
I've seen people on this board as low as free or $45/hour and as high as - well, the sky is the limit if you have a reputation that supports what you want to charge.