You might check the "sleep" covers available on eBay, AliBaba, Amazon, etc. to see if you can find some in your price range... Some protect the bezel on all sides even when open, and I know there's at least a few (like the one I have) that fully protect the sides with only tiny cutouts for power/USB. ('Sleep' covers have a magnet the keeps the cover securely closed when the Kobo isn't being used.)
Here's pics of the two types I'm trying to describe:
One similar to mine
One that (appears to?) cover all sides even when open