I don't have a whole lot of experience with the national networks, but I will try to answer your question. There were a few times when the national networks would contact the local station looking for video when we would have big tornado days in our viewing area. The national networks will usually come looking for video if it is a big day when houses get hit. This is how I got introduced to the national networks. The local station fed the video and my contact information via the satellite truck to some sort of wire service or something like that where all the national networks can view your video. I started getting calls from networks that were interested and you give them your terms and price. They decide if they want to do it or not and that is about it. After this first deal, the people I worked with at the networks gave me their number and told me to call them when I had video, so now I can go straight to them instead of going through the local station. I don't know how you could go about getting ahold of them for your first time other than working through a local network.
There isn't really a contract. They will fax you some stuff to sign. A 10 day license for my video is what I was offering. Either the Weather Channel or CNN had a prepared contract that said I was selling them an infinite license for the footage. I just crossed it out and wrote 10 days before signing it. Just make sure you read any contracts carefully. TWC also makes you fill out a bunch of paper work.
How much you sell your video for depends on a lot of things. Some things that effect the price are damage caused by the incident, where it happened, how many people have video of it, which network you are dealing with, and quality of your video just to name a few. Time is of the essence if you are trying to sell to the national networks. It is very competitive. You can get more money out of the news networks than you can get out of the weather channel (at least that is the way it has been in my experience). If you get something incredible, like a house getting hit, you got them by the short and curleys and you can demand a lot more money. Whatever you do, don't let them hose you on the price. They will try to get it as cheap as they can. Don't be afraid to say no.
The quickest and easiest way to get video to the networks is to set up an FTP site. All you have to do then is find an internet connection, save the video to the site, contact the networks and have them take a look at it.
Don't get to hung up in trying to sell your video to the national networks. It is tough to do and doesn't work out more times than it does for one reason or another. It can be very stressful and put a damper on an otherwise great day.
