Nasa doesn't make that much. Lets say 20 Billion. You have to use a lot of this money to actually build and research the stuff Nasa does and gives out (lots of patents for NASA). Space shuttles are either replaced every time or 99% the cost of the actual space ship.
Now with all of that, you have to pay off tons of people more than they would receive from going public. You have GPS companies, Satellite based companies, Researchers, Navy, super photoshoppers, astronauts, etc.
You can't do it. Assume NASA can do all of its conspiracy stuff for 10 billion (it can't do that anyway), that only leaves 10 billion (this is an inflated sum to begin with) to bribe and cover up thousands of people. Let's be nice and say there are only 1000 people who know (it would have to be much higher). That is 10 million per person. You would get a lot more than 10 million per person for blabbing.