The key deciding factor is usage. If your primary use of a tablet is reading ebooks, then it's hard to go wrong with the Kindle line, particularly the bright, vivid Kindle Fire HD. It can play movies, it offers a decent Web browser and Netflix streaming -- plus the book reading experience is front and center in the user interface.
Source: Daily CameraWhile the Daily Camera article itself points to Android vs iOS, the argument presented is still valid. The main factor is not actually price, but usage. What is the tablet going to be used for ? The answer for most people is light browsing, e-book reading and entertainment, such as watching movies and listening to music. Thus, the exact requirements are very light and can be met with inexpensive tablet.