Once Trump is officially our Pub candidate for President, and enters into the general election campaign, he will get federal campaign money to spend, just as the Dem Prez candidate will get federal money too. Both get funded so Trump won’t have to expend that much of his own money during the general election part of the campaign. Same for the Dem.
You might remember that Obama didn’t take federal campaign funds during the 2008 general election, though he’d previously said he’d do so.
From what I recall, it’s because he would have been locked into that arbitrary level of spending (it’s part of accepting the deal).
With campaigns costing what they do today, I don’t blame any candidate for turning them down. I don’t see Trump taking federal funds for the same reason. On the other hand, look at how well he’s done on the pittance he’s spent so far.