If I'm calculating correctly, Amazon demands $19.30 fixed cost + $2.29 dynamic based on total price. So at $99 Amazons percentage would be a lot less than 40%.

I put some similar data into another publishers system and it calculates roughly a third of a $99 book would go to the author. (softcover; 400 pages of which 200 are in color) Tax would further reduce the profit.

If it's put on KDP and using their print on demand, it works approximately as follows:

The cost of the printing of the book is subtracted.

You then get 60% of what is left.

The only way amazon's percentage will reduce below 40% is if you print the book through another source and sell it on Amazon as a platform. Then you're going to need to manage inventory.

Source: editing, typesetting and researching self-publishing for a friend who's going through this process right now.