Co-author here. We find it to be ok price for us.

- Quantitative evidence, we have over 150+ pre-orders in the last 3 month which is more than good for us. No advertising, no social media. We sold first book 700 times. So that's 100-120 people out of 700 who pre-ordered second book.

- Qualitative evidence. We have way more polite customers after raising price in the past ($49 -> $99) for our first book. More polite emails, more feedback and less emails asking for support.

EDIT: My co-author says that we have evidence that higher percentage of people who bought the book at higher price point actually read it.

PS: Price will go to $199 on Sunday midnight PST, that's when pre-order period ends.