Angel investors and incubators provide basically the same service, but rarely for books. I wonder why that is? There have been a number of books/series that I can think of that have spawned $100M+ valuations - Harry Potter, Hunger Games, 50 shades of gray, Jurassic Park, Song of Ice and Fire. If you include comics, then the list just goes on: Superman, Spiderman, Batman, X-men, Watchmen, etc.