I looked all over - Walmart, Target, even Ross - and everything was either the wrong size or close to the same price as the official Amazon cases (I looked at more than just e-reader cases...I looked at any and every kind of case available). I checked out BN hoping to score one of those $5 Nook cases mentioned above, but that was a no-go as well.

I was ready to take Luvmy4brats' advice and use a potholder...LOL.
Then I found this:

Mine is black though. Only Amazon third-party sellers carry it. The seller I bought it from - "GaryCave" - offered a choice of red or black. I contacted them asking for black, and upon their reply, I ordered. Oddly enough, it's no longer listed by that seller. I'm not sure why. But other sellers are still offering it (in the red shown above).
It's a bit too tall, wide, and deep all around for the K79, but I knew that before I placed the order. So, while it's far from a perfect solution, it more than gets the job done for now. I wanted a case fairly quickly, and this will tide me over in the meantime until I can find something specifically for the K79 that doesn't cost an arm and leg.
I paid only $5 for this.
If anyone else is interested, I'll snap some pics. Just LMK. You probably won't be able to get it in black - I got lucky there - but you can't beat the price either way (it varies a bit depending on the seller, but it's pretty cheap in general).
Edit: Bestbuy.com (and probably other e-tailers as well) also carry this case.