From small donors in a general election Trump will get somewhere between $250 to $500 million. Trump can run a very effective campaign without spending a billion or more as we have witnessed.
The reality will be as always...a few swing states are where the money is spent.
That’s why Cruz was so problematic as a candidate, he was getting 17% in those states. Promising to use Cubanadian ju-jitsu to win them in November.