[Examples are for iPad, but you can find similarly good and cheap cases for Amazon Kindles, for example here and here.]
The good news is that along with tablets and ereaders getting much cheaper, so are cases, in the last year or two.
The "bad" news is that not all of them are great, you are still advised to read a few reviews before pressing Buy.
See this pretty case for example:
... Just from the picture and description and price, what's not to like?
But then when you check the reviews:
"This is the worst iPad case I have ever seen, covers the screen,can't see the home button, cover is to big, sleep magnet does not work, only good thing about this is the pen at least that works. Complete waste of money, it also smells of cheap plastic."
"Not the best case as it doesn't fit well especially around the home button which the cut out area doesn't seem big enough for. Makes it difficult to press home button. Also the magnetic catch on cover is. It strong enough so the sleep function didn't work. Colour nice and pen ok."
"Very flimsy case and auto lock function does not work as stated and case does not lie flush with iPad."
So... maybe skip this one.
On the other hand, some are making quality at low prices, for example a new English company called JammyLizard (for some obscure reason) has me all agaga. They prices are rock bottom (cheaper at Amazon UK than at their own site), and yet they are some of the best cases I have tried.
I own and love their Horizon case:
It is precision-built, very light-weight (200 grams), looks good, and it cost only eight Pounds Sterling! (Say 12 bucks).
These are not yet on Amazon USA, but it's easy to buy from Amazon UK, you can even use the login you're used to. And shipping is cheap these days too, and with these prices you may not even have to pay import tax! (At least not if you only buy one at a time.)
I could not resist, I have also bought their "[faux] Leather Ultra Slim Full Body Smart Case":
|It looks and feel even better than the Horizon, and is about as cheap.|
Only downsize I see so far is that it's about 400 grams.