you may want to read this
http://en.wikipedia.org/wiki/Unlawful_Internet_Gambling_Enforcement_Act_of_2006 and then check with a good lawyer. You could also do a fantasy sports twist on it to keep it safe. You probably want to look into fantasy golf or fantasy mma as a model as both sports are mainly for individual athletes but the sites that offer allow you to draft a "team" that earns points based on certain stats, actions or other live game events.
but yeah its very costly to get started, at least for my niche which is kinda like what you want to do. also you should read about how sports books works and understand stuff like "overlay" good luck, feel free to hit me up.