trust me, I'm still trying to figure this whole thing out too, BUT these are the things that I have found to be true so far...
1) someone has to pay for your segment. be it you or your sponsors, whoever has the cash. (I've heard 10 to 15k for companies like level 1, and upwards of 120k for companies like warren miller)
2) paying for a segment doesn't guarantee you shots. typically companies will sponsor a movie and the contract will say that there can be a certain number of athletes allowed to film, usually 1 to 3. so the sponsorship money doesnt guarantee a segment, it basically gives an opportunity. if you or your sponsor pays for a segment you have to be willing to travel to wherever the company is filming; you or your sponsors pay for the travel, not the film company. And you may not be invited on a majority of the trips anyway, thats up to the film company
3) If you travel everywhere with the film company you have a higher chance of getting more shots, still not guaranteed. Much of your footage will end up being cut out in editing. If someone does a better trick than you, cut. if someone else's tricks were filmed better, yours gets cut.
4) even if you have the money to pay for a segment, you are not guaranteed the right to film. most companies have a profile they are trying to fill, they hand select the athletes to create the best movies possible. if you are a copy of, or similar(style and tricks wise) to someone else they film with, its highly unlikely that you'll be given the opportunity to film.
again, not true for everything, but these are just a few things I've learned along the way