If you publish your book via Kindle Direct Publishing, you can enrol in KDP Select. This means when readers read you books from Kindle Unlimited and the Kindle Owners' Lending Library you earn a share of the KDP Select Global Fund. Plus, you get extra royalties from customers in some countries. KDP is free to enrol in and you can reach a lot more readers without costing extra.
You can also utilize Amazon Advertising to get your book out there. With Amazon Advertising you set a budget and only pay when a shopper clicks your ad.
There are also several Price Promotions you can run. A Kindle Countdown deal gradually reduces the cost of your book, then when finished your book reverts to the original price. Only KDP books are eligible. You can also do a free book promotion. This is great if you have a trilogy or a series of books. You can make the first one free for a period and hopefully people will like it enough to then buy the remaining books in the series.
I recently did a free promo on "The Fallen" and left "The Guardians" and "Child of a Guardian and of the Free" at 2.99. I have now reduced the price of the books to stand at 99 cents each. Here is the Amazon link if you want to take a look at them.
https://www.amazon.com/-/e/B00KRYRPU2 (currently 99 cents each)
When I release "The Free" (which will be very soon) it will also be available at 99 cents.
If you are a new author, chances are you are unknown and you may need to start by setting a low price. Have a look on Amazon at the huge number of great books available for only 99 cents. If you have already acquired the fame of JK Rowling, you might like to start your book at a higher price.