Well... First welcome to CD. FIRST is a really amazing program and i think you will really enjoy it. Yeah its also pretty expensive (roughly $10,000). Aim for large cooperations and local business. One thing you might want to do is create sponsor packets and mail them to a bunch of companies and see who responds, however nothing beats a little face to face salesmanship. Also this mantra will help fundraiser fundraiser fundraiser!
I really wish you good luck!