The short answer
For most ebooks: $3.99–$6.99. For most paperbacks: $12.99–$18.99, depending on page count. If you want one number to start from and adjust, ebook $4.99 is the least-wrong default in most non-fiction and genre fiction categories.
Why the royalty band decides it
Kindle pays a 70% royalty on ebooks priced between $2.99 and $9.99, and 35% outside that range. The consequence is stark: a book at $2.99 earns roughly $2.09, while the same book at $1.99 earns about $0.70. You have to sell three copies at $1.99 to match one at $2.99. Below $2.99 you are not competing on price so much as donating margin.
The same cliff exists at the top. A $9.99 book earns about $6.99; at $10.99 the royalty drops to 35% and you earn about $3.85 — less money from a higher price. Unless your book is genuinely a reference work with a professional buyer, $9.99 is a ceiling rather than a milestone.
Print pricing works backwards
Paperbacks start from print cost, which is driven by page count. Print-on-demand takes its cut first, so a 300-page paperback has a hard floor beneath which you simply lose money. Work out the print cost, add the margin you want, then check the result against what comparable books in your category charge. If those two numbers are far apart, the problem is usually the page count or the trim size, not your ambition.
The $0.99 trap. It's a legitimate launch tactic and a legitimate price for book one of a series. It is not a permanent price for a standalone book. At 35% royalty you earn about 35 cents a copy, and — more damaging — readers use price as a quality signal. A permanently 99-cent standalone reads as a book nobody valued, including its author.
Check the shelf you're actually on
Before settling, look at the ten books that would sit beside yours: same category, similar length, published in the last two years. Not the bestsellers — the ordinary working books. That range is what your reader has been trained to expect. You can sit at the top of it with a strong cover and good reviews. Sitting far above it without those is how books stop selling.
Price is a lever, not a decision
Nothing here is permanent. Most authors test a price for 30–60 days, watch conversion rather than raw sales, and adjust once. What matters far more than the starting number is that your cover and description carry the price you've chosen — a $6.99 price with a $0.99 cover converts badly at any number.
If you'd rather see the whole picture — what publishing costs, what you'd earn per copy, and where you'd break even — the cost estimator lays it out in about thirty seconds, and marketing is where the price actually gets tested.