Is there an optimum price for selling or buying e-books.

Is there an optimum price at which to buy or sell Kindle editions through KDP?
If so, what is that price?

Perhaps contrary to popular opinion, I don’t think the majority of KDP’s books (Kindle) are bought on the strength of the author’s name, but because of the genre and price. Yes, readers will look for an author’s name on other titles once they have sampled their work and enjoyed it, but I feel in the first instance price will be a deciding factor. And genres such as Romance are attracting far more sales than any other genre.

Personally, because of my financial constraints on book purchases, I find myself drawn to the lower end of the price range (freebies to $2.99). A drop in the ocean as far as a good book is concerned.

I have bought e-books in the genre which I follow for $9.99 but then been disappointed and felt I was a little cheated.
What do you think?
Pic: Winter mist fills the Tamar Valley, Tasmania (from my window).