Here's the funny thing about Amazon: Because it's already selling you stuff, it has an easy way of knowing when a product category is starting to take off. Case in point: budget tablets. After reading lots of user reviews complaining about cheap, unreliable slates, the company had two major takeaways. One, people actually buy this crap and two, maybe Amazon can do better. That brings us to today's news: The outfit just introduced a 6-inch, $99 tablet, its least expensive yet. In addition, the company refreshed its $139 Kindle Fire HD 7 along with so-called Kids Edition models, which are basically the same 6- and 7-inch tablets, just with a two-year warranty and some robust parental controls. All of them start at under $200.