how "hard" of a case do you want?
I got this for my DX for 17$ free shipping
Amazon Link
Since the DX is so large the top straps cover a small part of the top screen and the power/volume buttons, but not an issue as it's still easy enough to access in the case by pushing it down (bottom staps are elastic)
IN k3, all of your controls are @ the bottom so it would be a nonissue, but it's 23$ for free supersaver shippiing, 18$ without =(
Amazon Link
Anyways, I like this case, it's cheap, it's decently made, and it feels decent in my hands when I'm using it. You can invert the zipper and zip it up to seal it up when you are using it as well. Also, the pocket is nice for storing the charger/usb cable/earphones if you like. You can also charge the kindle while it's in the case and zipped close.
Oh, and they have like 5 different colors, if you search for them >>
It's hard enough I think, it's vynil, with some memory foam, and it has an outer pocket to put stuff. It's not a "hard shell" though, and it's not EVA. Most hard cases just have a plastic/cardboard insert, so not sure what you are looking for.
Edit: think I found something for k3, which is more of what you are looking for
as long as you don't sit RIGHT ON IT, it should be ok...
The only problem with EVA is that it flexes in the middle if you put pressure right on it there. The corners are pretty rigid... the case is kind of shallow/thin so like I said it should do the job unless you put a lot of pressure right on the middle of the thing.
It's hard EVA case designed for k3 and not k2 like most of the others...
http://itgsm8.en.made-in-china.com/p...-Kindle-3.html
This would appear to be the product on amazon.com (im sure you can find others..)
http://www.amazon.com/Quality-Carryi...0675218&sr=8-2
Ah well with a little bit of searching, there you go: k3 EVA hard case