There are several settings I've run across, and a web search turned out why you want an ISBN from Bowker rather than one owned by someone else, and you probably want 10 ISBN's at US$295 rather than 1 ISBN at $125. I'm not particularly interested in repeating that discussion.
I do notice on the shipping cost calculator that there is a configurable "wholesale discount", and I believe I've heard that there is an option to have unsold books returned which is a bit of a deal-breaker outside of Amazon. I recall hearing one quote crossing the threshold of "Amazon will do business with you," and another, lower threshold of "regular bookstores will feel comfortable doing business with you, if for some reason they want to do so."
What is an optimal setting for a 1200 page book, 8 1/2 x 11", around $50 list price, so that ideally Amazon and small bookstores will feel comfortable dealing with it?