I would not do this through the riders. Have them put you in contact with their sponsor. If it's for the sponsor then you might as well cut out the middle man. Plus, the sponsor is where the money is. Bikers, like most athletes, probably don't have very full pockets and probably aren't stoked on paying for videos, etc.
As for price, it depends on what kind of video you're doing. No one will be able to give you a price because for all we know your video could be a 30 second commercial or a 5 minute mini-movie. What is the customer looking for?