One tip I have is to place all ebooks you want - no matter what the price - into your Amazon wishlist. Prices fluctuate all the time. Just yesterday I bought a book for just over £2 which was previously over £5. And the new Terry Brooks book was originally £16 has now come down to £9.99 although I'm waiting for the price to drop a little more before I purchase it.
Is there a way to get the Kindle prices to show on your wish list. I have loads of books in mine but have to keep going into each one and checking the price.