Why do you think you could print a 400 page full-color book for $5 and make a profit, especially at lowest volumes/print on demand? That stuff isn't just expensive because printing companies are evil.
I discovered that the economics of having things printed are surprising. It costs about the same to print one copy as it does to print a thousand copies. Nearly all the expense is in the setup, the marginal cost of paper is pretty small.
The trick is to correctly guess how many you'll need.
Why do you think you could print a 400 page full-color book for $5 and make a profit, especially at lowest volumes/print on demand? That stuff isn't just expensive because printing companies are evil.