On the news this morning, the head story seems to be that the US does not need the CIA. First thing that struck my mind, was the exact opposite. The agency is a self financed group, that may have established more than enough programs since Laos to be sitting pretty. That is perhaps where most gun running and drug smuggling affiliations were established. Not saying all associates of said agency are disfunctional, but who can deny they are not better off drifting to the shadow government. Where they can be of proper use and forgetten, nah.

Could the CIA exist on a "zero based buget"?

They will and can exist because most of their funding comes from black projects anyway so it wouldn't affect their real budget. The government siphoning they get is a small fraction of their actual costs so don't worry about them not getting enough money. As long as they're running coke for the Columbians and selling weapons to the Iranians/Chinese there will be plenty of intelligence to go around...sadly enough that is. They seem to be doing more harm to civilians with all of their nonsense than actually helping this country (along with most intelligence offices).